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 $67.28   11.499%   $75.0165   $75.02   $75.00   $75.00  
  Purchase #2 $210.68   7.256%   $225.9669   $225.97   $225.95   $226.00  
  Purchase #3 $111.76   6.224%   $118.7159   $118.72   $118.70   $118.70  
  Purchase #4 $240.34   6.346%   $255.592   $255.59   $255.60   $255.60  
  Purchase #5 $82.53   5.108%   $86.7456   $86.75   $86.75   $86.70  
  Purchase #6 $81.36   8.370%   $88.1698   $88.17   $88.15   $88.20  
  Purchase #7 $112.39   13.313%   $127.3525   $127.35   $127.35   $127.40  
  7 purchase totals = $906.34       $977.5592   $977.57   $977.50   $977.60