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 $83.28   9.619%   $91.2907   $91.29   $91.30   $91.30  
  Purchase #2 $202.36   5.281%   $213.0466   $213.05   $213.05   $213.00  
  Purchase #3 $58.55   8.698%   $63.6427   $63.64   $63.65   $63.60  
  Purchase #4 $10.51   10.153%   $11.5771   $11.58   $11.60   $11.60  
  Purchase #5 $209.58   3.123%   $216.1252   $216.13   $216.15   $216.10  
  Purchase #6 $102.73   4.165%   $107.0087   $107.01   $107.00   $107.00  
  Purchase #7 $64.93   9.329%   $70.9873   $70.99   $71.00   $71.00  
  7 purchase totals = $731.94       $773.6783   $773.69   $773.75   $773.60