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 $147.91   4.646%   $154.7819   $154.78   $154.80   $154.80  
  Purchase #2 $246.76   3.327%   $254.9697   $254.97   $254.95   $255.00  
  Purchase #3 $46.62   9.731%   $51.1566   $51.16   $51.15   $51.20  
  Purchase #4 $215.77   6.506%   $229.808   $229.81   $229.80   $229.80  
  Purchase #5 $68.90   10.819%   $76.3543   $76.35   $76.35   $76.40  
  Purchase #6 $13.87   12.386%   $15.5879   $15.59   $15.60   $15.60  
  Purchase #7 $191.89   5.528%   $202.4977   $202.50   $202.50   $202.50  
  7 purchase totals = $931.72       $985.1561   $985.16   $985.15   $985.30