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 $228.78   10.736%   $253.3418   $253.34   $253.35   $253.30  
  Purchase #2 $146.41   3.401%   $151.3894   $151.39   $151.40   $151.40  
  Purchase #3 $70.88   9.311%   $77.4796   $77.48   $77.50   $77.50  
  Purchase #4 $214.77   10.208%   $236.6937   $236.69   $236.70   $236.70  
  Purchase #5 $8.83   4.561%   $9.2327   $9.23   $9.25   $9.20  
  Purchase #6 $238.62   8.631%   $259.2153   $259.22   $259.20   $259.20  
  Purchase #7 $14.29   12.416%   $16.0642   $16.06   $16.05   $16.10  
  7 purchase totals = $922.58       $1,003.4167   $1,003.41   $1,003.45   $1,003.40