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	$100.74	8.494%	$109.2969	$109.30	$109.30	$109.30
Purchase #2	$233.64	13.246%	$264.588	$264.59	$264.60	$264.60
Purchase #3	$192.91	12.794%	$217.5909	$217.59	$217.60	$217.60
Purchase #4	$64.46	5.364%	$67.9176	$67.92	$67.90	$67.90
Purchase #5	$127.40	13.319%	$144.3684	$144.37	$144.35	$144.40
Purchase #6	$87.48	13.153%	$98.9862	$98.99	$99.00	$99.00
Purchase #7	$84.72	7.575%	$91.1375	$91.14	$91.15	$91.10
7 purchase totals =	$891.35		$993.8855	$993.90	$993.90	$993.90