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 $150.46   11.522%   $167.796   $167.80   $167.80   $167.80  
  Purchase #2 $211.34   13.427%   $239.7166   $239.72   $239.70   $239.70  
  Purchase #3 $64.98   7.863%   $70.0894   $70.09   $70.10   $70.10  
  Purchase #4 $42.29   5.169%   $44.476   $44.48   $44.50   $44.50  
  Purchase #5 $178.32   7.692%   $192.0364   $192.04   $192.05   $192.00  
  Purchase #6 $188.99   5.662%   $199.6906   $199.69   $199.70   $199.70  
  Purchase #7 $26.74   13.761%   $30.4197   $30.42   $30.40   $30.40  
  7 purchase totals = $863.12       $944.2247   $944.24   $944.25   $944.20