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	$250.48	12.425%	$281.6021	$281.60	$281.60	$281.60
Purchase #2	$229.26	5.628%	$242.1628	$242.16	$242.15	$242.20
Purchase #3	$26.50	7.383%	$28.4565	$28.46	$28.45	$28.50
Purchase #4	$61.93	8.590%	$67.2498	$67.25	$67.25	$67.20
Purchase #5	$111.95	11.133%	$124.4134	$124.41	$124.40	$124.40
Purchase #6	$120.85	7.201%	$129.5524	$129.55	$129.55	$129.60
Purchase #7	$79.38	4.423%	$82.891	$82.89	$82.90	$82.90
7 purchase totals =	$880.35		$956.3280	$956.32	$956.30	$956.40