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 $71.65   7.103%   $76.7393   $76.74   $76.75   $76.70  
  Purchase #2 $82.40   11.614%   $91.9699   $91.97   $91.95   $92.00  
  Purchase #3 $90.71   8.247%   $98.1909   $98.19   $98.20   $98.20  
  Purchase #4 $45.66   5.563%   $48.2001   $48.20   $48.20   $48.20  
  Purchase #5 $198.42   3.629%   $205.6207   $205.62   $205.60   $205.60  
  Purchase #6 $129.45   10.387%   $142.896   $142.90   $142.90   $142.90  
  Purchase #7 $236.52   12.122%   $265.191   $265.19   $265.20   $265.20  
  7 purchase totals = $854.81       $928.8079   $928.81   $928.80   $928.80