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	$140.78	12.445%	$158.3001	$158.30	$158.30	$158.30
Purchase #2	$234.55	8.167%	$253.7057	$253.71	$253.70	$253.70
Purchase #3	$187.29	4.872%	$196.4148	$196.41	$196.40	$196.40
Purchase #4	$10.79	11.460%	$12.0265	$12.03	$12.05	$12.00
Purchase #5	$171.49	7.259%	$183.9385	$183.94	$183.95	$183.90
Purchase #6	$216.37	12.452%	$243.3124	$243.31	$243.30	$243.30
Purchase #7	$17.74	5.500%	$18.7157	$18.72	$18.70	$18.70
7 purchase totals =	$979.01		$1,066.4137	$1,066.42	$1,066.40	$1,066.30