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	$28.78	13.353%	$32.623	$32.62	$32.60	$32.60
Purchase #2	$232.84	7.721%	$250.8176	$250.82	$250.80	$250.80
Purchase #3	$133.80	7.191%	$143.4216	$143.42	$143.40	$143.40
Purchase #4	$104.73	12.673%	$118.0024	$118.00	$118.00	$118.00
Purchase #5	$160.99	11.603%	$179.6697	$179.67	$179.65	$179.70
Purchase #6	$136.89	6.731%	$146.1041	$146.10	$146.10	$146.10
Purchase #7	$151.93	10.834%	$168.3901	$168.39	$168.40	$168.40
7 purchase totals =	$949.96		$1,039.0285	$1,039.02	$1,038.95	$1,039.00