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 $88.50   10.843%   $98.0961   $98.10   $98.10   $98.10  
  Purchase #2 $197.92   3.756%   $205.3539   $205.35   $205.35   $205.40  
  Purchase #3 $31.84   9.766%   $34.9495   $34.95   $34.95   $34.90  
  Purchase #4 $213.83   13.389%   $242.4597   $242.46   $242.45   $242.50  
  Purchase #5 $9.49   3.469%   $9.8192   $9.82   $9.80   $9.80  
  Purchase #6 $95.47   12.868%   $107.7551   $107.76   $107.75   $107.80  
  Purchase #7 $59.50   10.628%   $65.8237   $65.82   $65.80   $65.80  
  7 purchase totals = $696.55       $764.2572   $764.26   $764.20   $764.30