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 $82.75   11.414%   $92.1951   $92.20   $92.20   $92.20  
  Purchase #2 $67.50   6.532%   $71.9091   $71.91   $71.90   $71.90  
  Purchase #3 $64.71   4.426%   $67.5741   $67.57   $67.55   $67.60  
  Purchase #4 $209.75   3.779%   $217.6765   $217.68   $217.70   $217.70  
  Purchase #5 $62.39   4.237%   $65.0335   $65.03   $65.05   $65.00  
  Purchase #6 $48.75   7.794%   $52.5496   $52.55   $52.55   $52.50  
  Purchase #7 $232.80   4.856%   $244.1048   $244.10   $244.10   $244.10  
  7 purchase totals = $768.65       $811.0427   $811.04   $811.05   $811.00