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 $82.41   13.787%   $93.7719   $93.77   $93.75   $93.80  
  Purchase #2 $57.63   8.537%   $62.5499   $62.55   $62.55   $62.50  
  Purchase #3 $26.66   7.604%   $28.6872   $28.69   $28.70   $28.70  
  Purchase #4 $212.45   3.312%   $219.4863   $219.49   $219.50   $219.50  
  Purchase #5 $64.31   4.341%   $67.1017   $67.10   $67.10   $67.10  
  Purchase #6 $130.74   5.832%   $138.3648   $138.36   $138.35   $138.40  
  Purchase #7 $209.93   5.788%   $222.0807   $222.08   $222.10   $222.10  
  7 purchase totals = $784.13       $832.0425   $832.04   $832.05   $832.10