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	$221.41	13.325%	$250.9129	$250.91	$250.90	$250.90
Purchase #2	$88.86	6.320%	$94.476	$94.48	$94.50	$94.50
Purchase #3	$173.59	13.299%	$196.6757	$196.68	$196.70	$196.70
Purchase #4	$177.39	3.348%	$183.329	$183.33	$183.35	$183.30
Purchase #5	$98.75	11.574%	$110.1793	$110.18	$110.20	$110.20
Purchase #6	$143.59	3.547%	$148.6831	$148.68	$148.70	$148.70
Purchase #7	$127.37	11.713%	$142.2888	$142.29	$142.30	$142.30
7 purchase totals =	$1,030.96		$1,126.5448	$1,126.55	$1,126.65	$1,126.60