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 $136.72   11.408%   $152.317   $152.32   $152.30   $152.30  
  Purchase #2 $191.90   4.778%   $201.069   $201.07   $201.05   $201.10  
  Purchase #3 $74.73   13.293%   $84.6639   $84.66   $84.65   $84.70  
  Purchase #4 $118.95   13.250%   $134.7109   $134.71   $134.70   $134.70  
  Purchase #5 $12.70   9.437%   $13.8985   $13.90   $13.90   $13.90  
  Purchase #6 $163.85   4.335%   $170.9529   $170.95   $170.95   $171.00  
  Purchase #7 $212.61   13.203%   $240.6809   $240.68   $240.70   $240.70  
  7 purchase totals = $911.46       $998.2931   $998.29   $998.25   $998.40