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	$31.47	6.510%	$33.5187	$33.52	$33.50	$33.50
Purchase #2	$36.89	10.822%	$40.8822	$40.88	$40.90	$40.90
Purchase #3	$72.66	4.766%	$76.123	$76.12	$76.10	$76.10
Purchase #4	$177.41	3.414%	$183.4668	$183.47	$183.45	$183.50
Purchase #5	$193.49	9.284%	$211.4536	$211.45	$211.45	$211.50
Purchase #6	$155.96	3.422%	$161.297	$161.30	$161.30	$161.30
Purchase #7	$114.36	7.572%	$123.0193	$123.02	$123.00	$123.00
7 purchase totals =	$782.24		$829.7606	$829.76	$829.70	$829.80