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 $55.46   13.582%   $62.9926   $62.99   $63.00   $63.00  
  Purchase #2 $182.71   11.422%   $203.5791   $203.58   $203.60   $203.60  
  Purchase #3 $206.78   12.589%   $232.8115   $232.81   $232.80   $232.80  
  Purchase #4 $22.30   6.502%   $23.7499   $23.75   $23.75   $23.70  
  Purchase #5 $178.38   10.455%   $197.0296   $197.03   $197.05   $197.00  
  Purchase #6 $68.50   13.281%   $77.5975   $77.60   $77.60   $77.60  
  Purchase #7 $116.49   3.803%   $120.9201   $120.92   $120.90   $120.90  
  7 purchase totals = $830.62       $918.6803   $918.68   $918.70   $918.60