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 $62.92   13.760%   $71.5778   $71.58   $71.60   $71.60  
  Purchase #2 $234.35   8.168%   $253.4917   $253.49   $253.50   $253.50  
  Purchase #3 $79.84   5.395%   $84.1474   $84.15   $84.15   $84.10  
  Purchase #4 $76.94   5.592%   $81.2425   $81.24   $81.25   $81.20  
  Purchase #5 $198.99   4.452%   $207.849   $207.85   $207.85   $207.80  
  Purchase #6 $153.71   10.788%   $170.2922   $170.29   $170.30   $170.30  
  Purchase #7 $51.99   12.295%   $58.3822   $58.38   $58.40   $58.40  
  7 purchase totals = $858.74       $926.9828   $926.98   $927.05   $926.90