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	$57.38	13.656%	$65.2158	$65.22	$65.20	$65.20
Purchase #2	$116.43	3.103%	$120.0428	$120.04	$120.05	$120.00
Purchase #3	$198.50	12.135%	$222.588	$222.59	$222.60	$222.60
Purchase #4	$138.84	12.444%	$156.1172	$156.12	$156.10	$156.10
Purchase #5	$75.54	10.371%	$83.3743	$83.37	$83.35	$83.40
Purchase #6	$34.76	7.805%	$37.473	$37.47	$37.45	$37.50
Purchase #7	$51.92	6.582%	$55.3374	$55.34	$55.35	$55.30
7 purchase totals =	$673.37		$740.1485	$740.15	$740.10	$740.10