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	$159.56	7.109%	$170.9031	$170.90	$170.90	$170.90
Purchase #2	$151.50	13.346%	$171.7192	$171.72	$171.70	$171.70
Purchase #3	$55.69	11.751%	$62.2341	$62.23	$62.25	$62.20
Purchase #4	$220.73	4.121%	$229.8263	$229.83	$229.85	$229.80
Purchase #5	$172.97	13.859%	$196.9419	$196.94	$196.95	$196.90
Purchase #6	$180.96	4.603%	$189.2896	$189.29	$189.30	$189.30
Purchase #7	$125.46	9.437%	$137.2997	$137.30	$137.30	$137.30
7 purchase totals =	$1,066.87		$1,158.2139	$1,158.21	$1,158.25	$1,158.10