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 $66.48   3.714%   $68.9491   $68.95   $68.95   $68.90  
  Purchase #2 $201.98   9.230%   $220.6228   $220.62   $220.60   $220.60  
  Purchase #3 $206.73   13.541%   $234.7233   $234.72   $234.70   $234.70  
  Purchase #4 $51.27   5.689%   $54.1868   $54.19   $54.20   $54.20  
  Purchase #5 $88.55   11.630%   $98.8484   $98.85   $98.85   $98.80  
  Purchase #6 $26.71   4.627%   $27.9459   $27.95   $27.95   $27.90  
  Purchase #7 $39.51   3.739%   $40.9873   $40.99   $41.00   $41.00  
  7 purchase totals = $681.23       $746.2636   $746.27   $746.25   $746.10