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 $244.95   4.341%   $255.5833   $255.58   $255.60   $255.60  
  Purchase #2 $98.72   11.804%   $110.3729   $110.37   $110.35   $110.40  
  Purchase #3 $53.76   9.702%   $58.9758   $58.98   $59.00   $59.00  
  Purchase #4 $101.59   8.461%   $110.1855   $110.19   $110.20   $110.20  
  Purchase #5 $162.96   7.155%   $174.6198   $174.62   $174.60   $174.60  
  Purchase #6 $132.71   12.576%   $149.3996   $149.40   $149.40   $149.40  
  Purchase #7 $132.28   9.851%   $145.3109   $145.31   $145.30   $145.30  
  7 purchase totals = $926.97       $1,004.4478   $1,004.45   $1,004.45   $1,004.50