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 $116.54   8.556%   $126.5112   $126.51   $126.50   $126.50  
  Purchase #2 $202.37   7.867%   $218.2904   $218.29   $218.30   $218.30  
  Purchase #3 $61.63   3.862%   $64.0102   $64.01   $64.00   $64.00  
  Purchase #4 $247.47   13.820%   $281.6704   $281.67   $281.65   $281.70  
  Purchase #5 $121.70   12.736%   $137.1997   $137.20   $137.20   $137.20  
  Purchase #6 $225.98   8.516%   $245.2245   $245.22   $245.20   $245.20  
  Purchase #7 $32.46   6.430%   $34.5472   $34.55   $34.55   $34.50  
  7 purchase totals = $1,008.15       $1,107.4536   $1,107.45   $1,107.40   $1,107.40