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 $65.27   4.684%   $68.3272   $68.33   $68.35   $68.30  
  Purchase #2 $111.57   3.795%   $115.8041   $115.80   $115.80   $115.80  
  Purchase #3 $20.39   5.647%   $21.5414   $21.54   $21.55   $21.50  
  Purchase #4 $190.37   8.152%   $205.889   $205.89   $205.90   $205.90  
  Purchase #5 $167.63   13.464%   $190.1997   $190.20   $190.20   $190.20  
  Purchase #6 $60.55   3.395%   $62.6057   $62.61   $62.60   $62.60  
  Purchase #7 $247.57   11.489%   $276.0133   $276.01   $276.00   $276.00  
  7 purchase totals = $863.35       $940.3804   $940.38   $940.40   $940.30