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	$123.46	11.637%	$137.827	$137.83	$137.85	$137.80
Purchase #2	$31.88	4.490%	$33.3114	$33.31	$33.30	$33.30
Purchase #3	$81.68	11.252%	$90.8706	$90.87	$90.85	$90.90
Purchase #4	$52.93	11.459%	$58.9952	$59.00	$59.00	$59.00
Purchase #5	$159.66	3.439%	$165.1507	$165.15	$165.15	$165.20
Purchase #6	$60.78	8.317%	$65.8351	$65.84	$65.85	$65.80
Purchase #7	$219.55	10.844%	$243.358	$243.36	$243.35	$243.40
7 purchase totals =	$729.94		$795.3480	$795.36	$795.35	$795.40