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	$84.81	5.110%	$89.1438	$89.14	$89.15	$89.10
Purchase #2	$200.56	8.472%	$217.5514	$217.55	$217.55	$217.60
Purchase #3	$80.39	5.251%	$84.6113	$84.61	$84.60	$84.60
Purchase #4	$133.83	11.694%	$149.4801	$149.48	$149.50	$149.50
Purchase #5	$57.41	6.547%	$61.1686	$61.17	$61.15	$61.20
Purchase #6	$242.72	8.866%	$264.2396	$264.24	$264.25	$264.20
Purchase #7	$31.60	7.342%	$33.9201	$33.92	$33.90	$33.90
7 purchase totals =	$831.32		$900.1149	$900.11	$900.10	$900.10