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 $224.49   8.249%   $243.0082   $243.01   $243.00   $243.00  
  Purchase #2 $105.63   13.353%   $119.7348   $119.73   $119.75   $119.70  
  Purchase #3 $80.75   13.439%   $91.602   $91.60   $91.60   $91.60  
  Purchase #4 $38.28   13.745%   $43.5416   $43.54   $43.55   $43.50  
  Purchase #5 $96.42   11.177%   $107.1969   $107.20   $107.20   $107.20  
  Purchase #6 $203.31   9.398%   $222.4171   $222.42   $222.40   $222.40  
  Purchase #7 $208.50   4.158%   $217.1694   $217.17   $217.15   $217.20  
  7 purchase totals = $957.38       $1,044.6700   $1,044.67   $1,044.65   $1,044.60