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 $84.68   11.427%   $94.3564   $94.36   $94.35   $94.40  
  Purchase #2 $133.59   10.114%   $147.1013   $147.10   $147.10   $147.10  
  Purchase #3 $141.77   3.310%   $146.4626   $146.46   $146.45   $146.50  
  Purchase #4 $217.46   5.423%   $229.2529   $229.25   $229.25   $229.30  
  Purchase #5 $123.87   9.282%   $135.3676   $135.37   $135.35   $135.40  
  Purchase #6 $45.80   11.512%   $51.0725   $51.07   $51.05   $51.10  
  Purchase #7 $146.68   13.638%   $166.6842   $166.68   $166.70   $166.70  
  7 purchase totals = $893.85       $970.2975   $970.29   $970.25   $970.50