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	$167.85	13.130%	$189.8887	$189.89	$189.90	$189.90
Purchase #2	$44.30	8.169%	$47.9189	$47.92	$47.90	$47.90
Purchase #3	$53.46	11.136%	$59.4133	$59.41	$59.40	$59.40
Purchase #4	$97.52	13.299%	$110.4892	$110.49	$110.50	$110.50
Purchase #5	$83.77	7.639%	$90.1692	$90.17	$90.15	$90.20
Purchase #6	$233.63	6.803%	$249.5238	$249.52	$249.50	$249.50
Purchase #7	$245.28	4.498%	$256.3127	$256.31	$256.30	$256.30
7 purchase totals =	$925.81		$1,003.7158	$1,003.71	$1,003.65	$1,003.70