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	$158.91	6.684%	$169.5315	$169.53	$169.55	$169.50
Purchase #2	$60.39	11.800%	$67.516	$67.52	$67.50	$67.50
Purchase #3	$159.56	5.832%	$168.8655	$168.87	$168.85	$168.90
Purchase #4	$62.65	12.234%	$70.3146	$70.31	$70.30	$70.30
Purchase #5	$129.48	8.810%	$140.8872	$140.89	$140.90	$140.90
Purchase #6	$234.42	8.630%	$254.6504	$254.65	$254.65	$254.70
Purchase #7	$89.40	8.628%	$97.1134	$97.11	$97.10	$97.10
7 purchase totals =	$894.81		$968.8786	$968.88	$968.85	$968.90