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 $58.50   4.734%   $61.2694   $61.27   $61.25   $61.30  
  Purchase #2 $18.47   9.286%   $20.1851   $20.19   $20.20   $20.20  
  Purchase #3 $112.62   11.796%   $125.9047   $125.90   $125.90   $125.90  
  Purchase #4 $75.98   4.486%   $79.3885   $79.39   $79.40   $79.40  
  Purchase #5 $167.44   6.492%   $178.3102   $178.31   $178.30   $178.30  
  Purchase #6 $241.31   12.391%   $271.2107   $271.21   $271.20   $271.20  
  Purchase #7 $71.45   7.151%   $76.5594   $76.56   $76.55   $76.60  
  7 purchase totals = $745.77       $812.8280   $812.83   $812.80   $812.90