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 $237.98   11.754%   $265.9522   $265.95   $265.95   $266.00  
  Purchase #2 $22.79   9.591%   $24.9758   $24.98   $25.00   $25.00  
  Purchase #3 $95.95   11.273%   $106.7664   $106.77   $106.75   $106.80  
  Purchase #4 $101.65   8.821%   $110.6165   $110.62   $110.60   $110.60  
  Purchase #5 $50.97   9.834%   $55.9824   $55.98   $56.00   $56.00  
  Purchase #6 $153.53   4.639%   $160.6523   $160.65   $160.65   $160.70  
  Purchase #7 $156.56   9.365%   $171.2218   $171.22   $171.20   $171.20  
  7 purchase totals = $819.43       $896.1674   $896.17   $896.15   $896.30