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 $56.55   10.643%   $62.5686   $62.57   $62.55   $62.60  
  Purchase #2 $202.70   9.658%   $222.2768   $222.28   $222.30   $222.30  
  Purchase #3 $149.45   10.384%   $164.9689   $164.97   $164.95   $165.00  
  Purchase #4 $242.50   11.453%   $270.2735   $270.27   $270.25   $270.30  
  Purchase #5 $61.82   10.310%   $68.1936   $68.19   $68.20   $68.20  
  Purchase #6 $226.95   7.872%   $244.8155   $244.82   $244.80   $244.80  
  Purchase #7 $191.34   12.456%   $215.1733   $215.17   $215.15   $215.20  
  7 purchase totals = $1,131.31       $1,248.2702   $1,248.27   $1,248.20   $1,248.40