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 $53.32   12.436%   $59.9509   $59.95   $59.95   $60.00  
  Purchase #2 $76.37   10.293%   $84.2308   $84.23   $84.25   $84.20  
  Purchase #3 $13.49   11.313%   $15.0161   $15.02   $15.00   $15.00  
  Purchase #4 $233.36   9.791%   $256.2083   $256.21   $256.20   $256.20  
  Purchase #5 $249.95   3.155%   $257.8359   $257.84   $257.85   $257.80  
  Purchase #6 $43.40   10.857%   $48.1119   $48.11   $48.10   $48.10  
  Purchase #7 $211.81   8.364%   $229.5258   $229.53   $229.55   $229.50  
  7 purchase totals = $881.70       $950.8797   $950.89   $950.90   $950.80