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	$40.32	4.464%	$42.1199	$42.12	$42.10	$42.10
Purchase #2	$130.53	12.207%	$146.4638	$146.46	$146.45	$146.50
Purchase #3	$94.87	7.693%	$102.1683	$102.17	$102.15	$102.20
Purchase #4	$194.52	12.657%	$219.1404	$219.14	$219.15	$219.10
Purchase #5	$245.80	6.472%	$261.7082	$261.71	$261.70	$261.70
Purchase #6	$80.47	3.463%	$83.2567	$83.26	$83.25	$83.30
Purchase #7	$230.82	8.328%	$250.0427	$250.04	$250.05	$250.00
7 purchase totals =	$1,017.33		$1,104.9000	$1,104.90	$1,104.85	$1,104.90