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 $162.73   13.272%   $184.3275   $184.33   $184.35   $184.30  
  Purchase #2 $90.94   11.434%   $101.3381   $101.34   $101.35   $101.30  
  Purchase #3 $80.69   6.662%   $86.0656   $86.07   $86.05   $86.10  
  Purchase #4 $59.55   8.299%   $64.4921   $64.49   $64.50   $64.50  
  Purchase #5 $235.30   9.623%   $257.9429   $257.94   $257.95   $257.90  
  Purchase #6 $126.87   11.459%   $141.408   $141.41   $141.40   $141.40  
  Purchase #7 $45.71   8.425%   $49.5611   $49.56   $49.55   $49.60  
  7 purchase totals = $801.79       $885.1353   $885.14   $885.15   $885.10