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 $55.70   13.792%   $63.3821   $63.38   $63.40   $63.40  
  Purchase #2 $208.73   4.466%   $218.0519   $218.05   $218.05   $218.10  
  Purchase #3 $60.28   3.699%   $62.5098   $62.51   $62.50   $62.50  
  Purchase #4 $158.32   8.463%   $171.7186   $171.72   $171.70   $171.70  
  Purchase #5 $51.57   6.591%   $54.969   $54.97   $54.95   $55.00  
  Purchase #6 $122.47   13.225%   $138.6667   $138.67   $138.65   $138.70  
  Purchase #7 $58.30   3.261%   $60.2012   $60.20   $60.20   $60.20  
  7 purchase totals = $715.37       $769.4993   $769.50   $769.45   $769.60