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	$57.53	11.808%	$64.3231	$64.32	$64.30	$64.30
Purchase #2	$226.39	7.679%	$243.7745	$243.77	$243.75	$243.80
Purchase #3	$124.76	5.231%	$131.2862	$131.29	$131.30	$131.30
Purchase #4	$217.55	11.561%	$242.701	$242.70	$242.70	$242.70
Purchase #5	$192.66	3.363%	$199.1392	$199.14	$199.15	$199.10
Purchase #6	$94.38	13.234%	$106.8702	$106.87	$106.85	$106.90
Purchase #7	$71.36	10.444%	$78.8128	$78.81	$78.80	$78.80
7 purchase totals =	$984.63		$1,066.9070	$1,066.90	$1,066.85	$1,066.90