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	$114.41	8.620%	$124.2721	$124.27	$124.25	$124.30
Purchase #2	$89.33	11.857%	$99.9219	$99.92	$99.90	$99.90
Purchase #3	$202.70	13.300%	$229.6591	$229.66	$229.65	$229.70
Purchase #4	$136.83	4.743%	$143.3198	$143.32	$143.30	$143.30
Purchase #5	$11.64	11.304%	$12.9558	$12.96	$12.95	$13.00
Purchase #6	$127.50	10.150%	$140.4413	$140.44	$140.45	$140.40
Purchase #7	$202.48	7.580%	$217.828	$217.83	$217.85	$217.80
7 purchase totals =	$884.89		$968.3980	$968.40	$968.35	$968.40