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 $67.97   11.685%   $75.9123   $75.91   $75.90   $75.90  
  Purchase #2 $136.39   13.220%   $154.4208   $154.42   $154.40   $154.40  
  Purchase #3 $128.69   3.149%   $132.7424   $132.74   $132.75   $132.70  
  Purchase #4 $229.46   3.464%   $237.4085   $237.41   $237.40   $237.40  
  Purchase #5 $76.83   12.795%   $86.6604   $86.66   $86.65   $86.70  
  Purchase #6 $101.42   7.763%   $109.2932   $109.29   $109.30   $109.30  
  Purchase #7 $142.37   3.222%   $146.9572   $146.96   $146.95   $147.00  
  7 purchase totals = $883.13       $943.3948   $943.39   $943.35   $943.40