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 $57.82   6.758%   $61.7275   $61.73   $61.75   $61.70  
  Purchase #2 $225.25   13.548%   $255.7669   $255.77   $255.75   $255.80  
  Purchase #3 $44.71   4.538%   $46.7389   $46.74   $46.75   $46.70  
  Purchase #4 $151.88   12.389%   $170.6964   $170.70   $170.70   $170.70  
  Purchase #5 $133.89   7.684%   $144.1781   $144.18   $144.20   $144.20  
  Purchase #6 $71.92   4.235%   $74.9658   $74.97   $74.95   $75.00  
  Purchase #7 $218.69   11.119%   $243.0061   $243.01   $243.00   $243.00  
  7 purchase totals = $904.16       $997.0797   $997.10   $997.10   $997.10