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 $150.68   7.504%   $161.987   $161.99   $162.00   $162.00  
  Purchase #2 $140.83   7.694%   $151.6655   $151.67   $151.65   $151.70  
  Purchase #3 $64.81   10.474%   $71.5982   $71.60   $71.60   $71.60  
  Purchase #4 $228.63   9.634%   $250.6562   $250.66   $250.65   $250.70  
  Purchase #5 $71.26   11.864%   $79.7143   $79.71   $79.70   $79.70  
  Purchase #6 $18.34   12.275%   $20.5912   $20.59   $20.60   $20.60  
  Purchase #7 $59.73   8.323%   $64.7013   $64.70   $64.70   $64.70  
  7 purchase totals = $734.28       $800.9137   $800.92   $800.90   $801.00