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 $241.84   7.486%   $259.9441   $259.94   $259.95   $259.90  
  Purchase #2 $126.64   11.416%   $141.0972   $141.10   $141.10   $141.10  
  Purchase #3 $166.82   10.589%   $184.4846   $184.48   $184.50   $184.50  
  Purchase #4 $62.67   7.410%   $67.3138   $67.31   $67.30   $67.30  
  Purchase #5 $46.25   4.588%   $48.372   $48.37   $48.35   $48.40  
  Purchase #6 $66.87   13.412%   $75.8386   $75.84   $75.85   $75.80  
  Purchase #7 $102.59   9.344%   $112.176   $112.18   $112.20   $112.20  
  7 purchase totals = $813.68       $889.2263   $889.22   $889.25   $889.20