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 $66.62   10.858%   $73.8536   $73.85   $73.85   $73.90  
  Purchase #2 $111.27   9.473%   $121.8106   $121.81   $121.80   $121.80  
  Purchase #3 $100.74   13.718%   $114.5595   $114.56   $114.55   $114.60  
  Purchase #4 $78.53   9.175%   $85.7351   $85.74   $85.75   $85.70  
  Purchase #5 $153.36   11.525%   $171.0347   $171.03   $171.05   $171.00  
  Purchase #6 $231.54   8.865%   $252.066   $252.07   $252.05   $252.10  
  Purchase #7 $117.54   6.171%   $124.7934   $124.79   $124.80   $124.80  
  7 purchase totals = $859.60       $943.8529   $943.85   $943.85   $943.90