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 $41.53   7.183%   $44.5131   $44.51   $44.50   $44.50  
  Purchase #2 $119.88   3.187%   $123.7006   $123.70   $123.70   $123.70  
  Purchase #3 $15.55   9.215%   $16.9829   $16.98   $17.00   $17.00  
  Purchase #4 $237.53   13.574%   $269.7723   $269.77   $269.75   $269.80  
  Purchase #5 $215.77   9.726%   $236.7558   $236.76   $236.75   $236.80  
  Purchase #6 $118.40   11.210%   $131.6726   $131.67   $131.65   $131.70  
  Purchase #7 $68.34   9.644%   $74.9307   $74.93   $74.95   $74.90  
  7 purchase totals = $817.00       $898.3280   $898.32   $898.30   $898.40