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 $88.69   5.527%   $93.5919   $93.59   $93.60   $93.60  
  Purchase #2 $190.58   8.367%   $206.5258   $206.53   $206.55   $206.50  
  Purchase #3 $15.50   11.579%   $17.2947   $17.29   $17.30   $17.30  
  Purchase #4 $229.91   5.836%   $243.3275   $243.33   $243.35   $243.30  
  Purchase #5 $184.25   12.793%   $207.8211   $207.82   $207.80   $207.80  
  Purchase #6 $179.80   5.560%   $189.7969   $189.80   $189.80   $189.80  
  Purchase #7 $17.62   9.842%   $19.3542   $19.35   $19.35   $19.40  
  7 purchase totals = $906.35       $977.7121   $977.71   $977.75   $977.70