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	$20.84	3.224%	$21.5119	$21.51	$21.50	$21.50
Purchase #2	$214.54	12.499%	$241.3554	$241.36	$241.35	$241.40
Purchase #3	$78.62	5.755%	$83.1446	$83.14	$83.15	$83.10
Purchase #4	$198.62	8.135%	$214.7777	$214.78	$214.80	$214.80
Purchase #5	$154.67	8.244%	$167.421	$167.42	$167.40	$167.40
Purchase #6	$89.92	10.797%	$99.6287	$99.63	$99.65	$99.60
Purchase #7	$100.82	3.259%	$104.1057	$104.11	$104.10	$104.10
7 purchase totals =	$858.03		$931.9450	$931.95	$931.95	$931.90