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 $149.68   10.394%   $165.2377   $165.24   $165.25   $165.20  
  Purchase #2 $68.70   7.591%   $73.915   $73.92   $73.90   $73.90  
  Purchase #3 $162.28   8.153%   $175.5107   $175.51   $175.50   $175.50  
  Purchase #4 $10.44   8.299%   $11.3064   $11.31   $11.30   $11.30  
  Purchase #5 $242.68   6.560%   $258.5998   $258.60   $258.60   $258.60  
  Purchase #6 $225.57   9.323%   $246.5999   $246.60   $246.60   $246.60  
  Purchase #7 $120.56   8.786%   $131.1524   $131.15   $131.15   $131.20  
  7 purchase totals = $979.91       $1,062.3219   $1,062.33   $1,062.30   $1,062.30