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	$155.33	8.160%	$168.0049	$168.00	$168.00	$168.00
Purchase #2	$235.81	7.366%	$253.1798	$253.18	$253.20	$253.20
Purchase #3	$172.45	6.602%	$183.8351	$183.84	$183.85	$183.80
Purchase #4	$89.47	11.136%	$99.4334	$99.43	$99.45	$99.40
Purchase #5	$133.85	4.607%	$140.0165	$140.02	$140.00	$140.00
Purchase #6	$129.86	6.140%	$137.8334	$137.83	$137.85	$137.80
Purchase #7	$63.61	11.563%	$70.9652	$70.97	$70.95	$71.00
7 purchase totals =	$980.38		$1,053.2683	$1,053.27	$1,053.30	$1,053.20