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 $247.69   5.642%   $261.6647   $261.66   $261.65   $261.70  
  Purchase #2 $90.85   7.607%   $97.761   $97.76   $97.75   $97.80  
  Purchase #3 $35.54   11.144%   $39.5006   $39.50   $39.50   $39.50  
  Purchase #4 $99.79   6.688%   $106.464   $106.46   $106.45   $106.50  
  Purchase #5 $25.68   12.707%   $28.9432   $28.94   $28.95   $28.90  
  Purchase #6 $145.99   4.121%   $152.0062   $152.01   $152.00   $152.00  
  Purchase #7 $109.89   11.508%   $122.5361   $122.54   $122.55   $122.50  
  7 purchase totals = $755.43       $808.8758   $808.87   $808.85   $808.90