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 $49.50   3.416%   $51.1909   $51.19   $51.20   $51.20  
  Purchase #2 $218.26   10.184%   $240.4876   $240.49   $240.50   $240.50  
  Purchase #3 $244.49   6.340%   $259.9907   $259.99   $260.00   $260.00  
  Purchase #4 $158.97   6.252%   $168.9088   $168.91   $168.90   $168.90  
  Purchase #5 $218.90   4.722%   $229.2365   $229.24   $229.25   $229.20  
  Purchase #6 $162.46   10.484%   $179.4923   $179.49   $179.50   $179.50  
  Purchase #7 $34.43   8.512%   $37.3607   $37.36   $37.35   $37.40  
  7 purchase totals = $1,087.01       $1,166.6675   $1,166.67   $1,166.70   $1,166.70