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 $184.56   12.497%   $207.6245   $207.62   $207.60   $207.60  
  Purchase #2 $193.96   9.126%   $211.6608   $211.66   $211.65   $211.70  
  Purchase #3 $30.96   13.818%   $35.2381   $35.24   $35.25   $35.20  
  Purchase #4 $158.25   10.492%   $174.8536   $174.85   $174.85   $174.90  
  Purchase #5 $59.40   7.567%   $63.8948   $63.89   $63.90   $63.90  
  Purchase #6 $119.56   5.464%   $126.0928   $126.09   $126.10   $126.10  
  Purchase #7 $19.74   13.396%   $22.3844   $22.38   $22.40   $22.40  
  7 purchase totals = $766.43       $841.7490   $841.73   $841.75   $841.80