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 $58.64   10.174%   $64.606   $64.61   $64.60   $64.60  
  Purchase #2 $225.57   5.463%   $237.8929   $237.89   $237.90   $237.90  
  Purchase #3 $14.68   12.316%   $16.488   $16.49   $16.50   $16.50  
  Purchase #4 $157.93   3.493%   $163.4465   $163.45   $163.45   $163.40  
  Purchase #5 $144.57   5.540%   $152.5792   $152.58   $152.60   $152.60  
  Purchase #6 $113.63   11.109%   $126.2532   $126.25   $126.25   $126.30  
  Purchase #7 $194.51   11.649%   $217.1685   $217.17   $217.15   $217.20  
  7 purchase totals = $909.53       $978.4343   $978.44   $978.45   $978.50