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 $132.48   5.694%   $140.0234   $140.02   $140.00   $140.00  
  Purchase #2 $10.88   6.111%   $11.5449   $11.54   $11.55   $11.50  
  Purchase #3 $91.26   4.429%   $95.3019   $95.30   $95.30   $95.30  
  Purchase #4 $197.81   4.195%   $206.1081   $206.11   $206.10   $206.10  
  Purchase #5 $91.49   6.534%   $97.468   $97.47   $97.45   $97.50  
  Purchase #6 $121.30   13.562%   $137.7507   $137.75   $137.75   $137.80  
  Purchase #7 $34.65   11.355%   $38.5845   $38.58   $38.60   $38.60  
  7 purchase totals = $679.87       $726.7815   $726.77   $726.75   $726.80