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 $70.41   10.211%   $77.5996   $77.60   $77.60   $77.60  
  Purchase #2 $112.81   8.859%   $122.8038   $122.80   $122.80   $122.80  
  Purchase #3 $228.93   11.558%   $255.3897   $255.39   $255.40   $255.40  
  Purchase #4 $238.28   12.684%   $268.5034   $268.50   $268.50   $268.50  
  Purchase #5 $116.36   7.754%   $125.3826   $125.38   $125.40   $125.40  
  Purchase #6 $234.98   8.793%   $255.6418   $255.64   $255.65   $255.60  
  Purchase #7 $182.37   9.346%   $199.4143   $199.41   $199.40   $199.40  
  7 purchase totals = $1,184.14       $1,304.7352   $1,304.72   $1,304.75   $1,304.70