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 $233.30   9.668%   $255.8554   $255.86   $255.85   $255.90  
  Purchase #2 $112.98   10.367%   $124.6926   $124.69   $124.70   $124.70  
  Purchase #3 $165.99   8.850%   $180.6801   $180.68   $180.70   $180.70  
  Purchase #4 $92.84   5.119%   $97.5925   $97.59   $97.60   $97.60  
  Purchase #5 $150.66   6.781%   $160.8763   $160.88   $160.90   $160.90  
  Purchase #6 $74.93   8.848%   $81.5598   $81.56   $81.55   $81.60  
  Purchase #7 $29.38   11.332%   $32.7093   $32.71   $32.70   $32.70  
  7 purchase totals = $860.08       $933.9660   $933.97   $934.00   $934.10