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 $222.44   10.617%   $246.0565   $246.06   $246.05   $246.10  
  Purchase #2 $194.56   11.758%   $217.4364   $217.44   $217.45   $217.40  
  Purchase #3 $236.29   8.865%   $257.2371   $257.24   $257.25   $257.20  
  Purchase #4 $10.35   10.826%   $11.4705   $11.47   $11.45   $11.50  
  Purchase #5 $158.42   12.640%   $178.4443   $178.44   $178.45   $178.40  
  Purchase #6 $133.78   5.395%   $140.9974   $141.00   $141.00   $141.00  
  Purchase #7 $201.31   3.732%   $208.8229   $208.82   $208.80   $208.80  
  7 purchase totals = $1,157.15       $1,260.4651   $1,260.47   $1,260.45   $1,260.40