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 $226.87   11.183%   $252.2409   $252.24   $252.25   $252.20  
  Purchase #2 $222.84   13.856%   $253.7167   $253.72   $253.70   $253.70  
  Purchase #3 $91.40   6.546%   $97.383   $97.38   $97.40   $97.40  
  Purchase #4 $73.49   7.447%   $78.9628   $78.96   $78.95   $79.00  
  Purchase #5 $89.72   13.849%   $102.1453   $102.15   $102.15   $102.10  
  Purchase #6 $87.89   3.827%   $91.2536   $91.25   $91.25   $91.30  
  Purchase #7 $71.93   10.710%   $79.6337   $79.63   $79.65   $79.60  
  7 purchase totals = $864.14       $955.3360   $955.33   $955.35   $955.30