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	$67.99	6.255%	$72.2428	$72.24	$72.25	$72.20
Purchase #2	$130.29	8.550%	$141.4298	$141.43	$141.45	$141.40
Purchase #3	$232.71	13.674%	$264.5308	$264.53	$264.55	$264.50
Purchase #4	$205.92	3.172%	$212.4518	$212.45	$212.45	$212.50
Purchase #5	$188.39	3.262%	$194.5353	$194.54	$194.55	$194.50
Purchase #6	$187.79	5.784%	$198.6518	$198.65	$198.65	$198.70
Purchase #7	$15.65	7.561%	$16.8333	$16.83	$16.85	$16.80
7 purchase totals =	$1,028.74		$1,100.6756	$1,100.67	$1,100.75	$1,100.60