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	$117.74	6.646%	$125.565	$125.57	$125.55	$125.60
Purchase #2	$37.31	13.489%	$42.3427	$42.34	$42.35	$42.30
Purchase #3	$59.27	13.843%	$67.4747	$67.47	$67.45	$67.50
Purchase #4	$18.46	10.393%	$20.3785	$20.38	$20.40	$20.40
Purchase #5	$124.73	10.820%	$138.2258	$138.23	$138.25	$138.20
Purchase #6	$49.28	12.195%	$55.2897	$55.29	$55.30	$55.30
Purchase #7	$195.50	5.512%	$206.276	$206.28	$206.30	$206.30
7 purchase totals =	$602.29		$655.5524	$655.56	$655.60	$655.60