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	$165.91	10.784%	$183.8017	$183.80	$183.80	$183.80
Purchase #2	$54.25	10.220%	$59.7944	$59.79	$59.80	$59.80
Purchase #3	$73.68	12.366%	$82.7913	$82.79	$82.80	$82.80
Purchase #4	$44.92	9.747%	$49.2984	$49.30	$49.30	$49.30
Purchase #5	$78.68	4.813%	$82.4669	$82.47	$82.45	$82.50
Purchase #6	$225.88	12.588%	$254.3138	$254.31	$254.30	$254.30
Purchase #7	$80.74	12.300%	$90.671	$90.67	$90.65	$90.70
7 purchase totals =	$724.06		$803.1375	$803.13	$803.10	$803.20