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	$139.27	6.204%	$147.9103	$147.91	$147.90	$147.90
Purchase #2	$220.45	12.260%	$247.4772	$247.48	$247.50	$247.50
Purchase #3	$150.51	9.177%	$164.3223	$164.32	$164.30	$164.30
Purchase #4	$91.63	8.637%	$99.5441	$99.54	$99.55	$99.50
Purchase #5	$71.69	13.327%	$81.2441	$81.24	$81.25	$81.20
Purchase #6	$70.72	8.577%	$76.7857	$76.79	$76.80	$76.80
Purchase #7	$78.61	8.598%	$85.3689	$85.37	$85.35	$85.40
7 purchase totals =	$822.88		$902.6526	$902.65	$902.65	$902.60