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	$125.51	10.246%	$138.3698	$138.37	$138.35	$138.40
Purchase #2	$236.72	13.834%	$269.4678	$269.47	$269.45	$269.50
Purchase #3	$51.39	11.479%	$57.2891	$57.29	$57.30	$57.30
Purchase #4	$171.41	10.460%	$189.3395	$189.34	$189.35	$189.30
Purchase #5	$144.77	7.512%	$155.6451	$155.65	$155.65	$155.60
Purchase #6	$75.90	3.369%	$78.4571	$78.46	$78.45	$78.50
Purchase #7	$126.91	13.375%	$143.8842	$143.88	$143.90	$143.90
7 purchase totals =	$932.61		$1,032.4526	$1,032.46	$1,032.45	$1,032.50