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	$25.37	8.179%	$27.445	$27.45	$27.45	$27.40
Purchase #2	$164.74	12.375%	$185.1266	$185.13	$185.15	$185.10
Purchase #3	$85.57	6.688%	$91.2929	$91.29	$91.30	$91.30
Purchase #4	$99.70	12.123%	$111.7866	$111.79	$111.80	$111.80
Purchase #5	$134.44	7.656%	$144.7327	$144.73	$144.75	$144.70
Purchase #6	$204.91	13.118%	$231.7901	$231.79	$231.80	$231.80
Purchase #7	$29.50	9.467%	$32.2928	$32.29	$32.30	$32.30
7 purchase totals =	$744.23		$824.4667	$824.47	$824.55	$824.40