Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $95.55   12.298%   $107.3007   $107.30   $107.30   $107.30  
  Purchase #2 $101.91   13.498%   $115.6658   $115.67   $115.65   $115.70  
  Purchase #3 $139.56   11.112%   $155.0679   $155.07   $155.05   $155.10  
  Purchase #4 $117.67   11.715%   $131.455   $131.46   $131.45   $131.50  
  Purchase #5 $199.49   3.414%   $206.3006   $206.30   $206.30   $206.30  
  Purchase #6 $185.78   11.784%   $207.6723   $207.67   $207.65   $207.70  
  Purchase #7 $238.75   13.441%   $270.8404   $270.84   $270.85   $270.80  
  7 purchase totals = $1,078.71       $1,194.3027   $1,194.31   $1,194.25   $1,194.40