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	$225.37	12.345%	$253.1919	$253.19	$253.20	$253.20
Purchase #2	$120.38	8.473%	$130.5798	$130.58	$130.60	$130.60
Purchase #3	$34.92	10.279%	$38.5094	$38.51	$38.50	$38.50
Purchase #4	$191.40	11.596%	$213.5947	$213.59	$213.60	$213.60
Purchase #5	$33.98	4.244%	$35.4221	$35.42	$35.40	$35.40
Purchase #6	$212.91	4.708%	$222.9338	$222.93	$222.95	$222.90
Purchase #7	$196.53	3.307%	$203.0292	$203.03	$203.05	$203.00
7 purchase totals =	$1,015.49		$1,097.2609	$1,097.25	$1,097.30	$1,097.20