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 $229.29   10.682%   $253.7828   $253.78   $253.80   $253.80  
  Purchase #2 $61.41   7.777%   $66.1859   $66.19   $66.20   $66.20  
  Purchase #3 $134.78   11.635%   $150.4617   $150.46   $150.45   $150.50  
  Purchase #4 $87.83   3.634%   $91.0217   $91.02   $91.00   $91.00  
  Purchase #5 $226.41   6.220%   $240.4927   $240.49   $240.50   $240.50  
  Purchase #6 $216.89   9.267%   $236.9892   $236.99   $237.00   $237.00  
  Purchase #7 $7.93   13.587%   $9.0074   $9.01   $9.00   $9.00  
  7 purchase totals = $964.54       $1,047.9414   $1,047.94   $1,047.95   $1,048.00