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 $157.96   12.166%   $177.1774   $177.18   $177.20   $177.20  
  Purchase #2 $169.47   6.177%   $179.9382   $179.94   $179.95   $179.90  
  Purchase #3 $232.67   10.426%   $256.9282   $256.93   $256.95   $256.90  
  Purchase #4 $174.78   7.863%   $188.523   $188.52   $188.50   $188.50  
  Purchase #5 $24.33   5.115%   $25.5745   $25.57   $25.55   $25.60  
  Purchase #6 $104.47   9.651%   $114.5524   $114.55   $114.55   $114.60  
  Purchase #7 $100.63   9.871%   $110.5632   $110.56   $110.55   $110.60  
  7 purchase totals = $964.31       $1,053.2569   $1,053.25   $1,053.25   $1,053.30