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	$130.91	10.589%	$144.7721	$144.77	$144.75	$144.80
Purchase #2	$54.64	13.155%	$61.8279	$61.83	$61.85	$61.80
Purchase #3	$9.40	12.409%	$10.5664	$10.57	$10.55	$10.60
Purchase #4	$100.25	13.862%	$114.1467	$114.15	$114.15	$114.10
Purchase #5	$81.79	4.260%	$85.2743	$85.27	$85.25	$85.30
Purchase #6	$209.48	3.749%	$217.3334	$217.33	$217.35	$217.30
Purchase #7	$28.67	12.319%	$32.2019	$32.20	$32.20	$32.20
7 purchase totals =	$615.14		$666.1227	$666.12	$666.10	$666.10