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	$27.77	6.385%	$29.5431	$29.54	$29.55	$29.50
Purchase #2	$120.91	13.874%	$137.6851	$137.69	$137.70	$137.70
Purchase #3	$89.51	8.249%	$96.8937	$96.89	$96.90	$96.90
Purchase #4	$223.81	8.586%	$243.0263	$243.03	$243.05	$243.00
Purchase #5	$150.65	3.160%	$155.4105	$155.41	$155.40	$155.40
Purchase #6	$107.73	9.685%	$118.1637	$118.16	$118.15	$118.20
Purchase #7	$79.83	3.275%	$82.4444	$82.44	$82.45	$82.40
7 purchase totals =	$800.21		$863.1668	$863.16	$863.20	$863.10