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	$179.56	9.260%	$196.1873	$196.19	$196.20	$196.20
Purchase #2	$158.26	7.590%	$170.2719	$170.27	$170.25	$170.30
Purchase #3	$214.57	3.653%	$222.4082	$222.41	$222.40	$222.40
Purchase #4	$89.45	7.150%	$95.8457	$95.85	$95.85	$95.80
Purchase #5	$197.72	12.335%	$222.1088	$222.11	$222.10	$222.10
Purchase #6	$185.43	13.297%	$210.0866	$210.09	$210.10	$210.10
Purchase #7	$126.65	12.111%	$141.9886	$141.99	$142.00	$142.00
7 purchase totals =	$1,151.64		$1,258.8971	$1,258.91	$1,258.90	$1,258.90