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	$172.40	7.349%	$185.0697	$185.07	$185.05	$185.10
Purchase #2	$158.36	13.544%	$179.8083	$179.81	$179.80	$179.80
Purchase #3	$232.41	10.330%	$256.418	$256.42	$256.40	$256.40
Purchase #4	$216.89	6.851%	$231.7491	$231.75	$231.75	$231.70
Purchase #5	$36.78	6.560%	$39.1928	$39.19	$39.20	$39.20
Purchase #6	$65.79	10.244%	$72.5295	$72.53	$72.55	$72.50
Purchase #7	$118.61	8.149%	$128.2755	$128.28	$128.30	$128.30
7 purchase totals =	$1,001.24		$1,093.0429	$1,093.05	$1,093.05	$1,093.00