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	$38.82	3.560%	$40.202	$40.20	$40.20	$40.20
Purchase #2	$126.88	13.203%	$143.632	$143.63	$143.65	$143.60
Purchase #3	$28.50	13.769%	$32.4242	$32.42	$32.40	$32.40
Purchase #4	$16.44	4.279%	$17.1435	$17.14	$17.15	$17.10
Purchase #5	$78.59	13.460%	$89.1682	$89.17	$89.15	$89.20
Purchase #6	$175.50	13.821%	$199.7559	$199.76	$199.75	$199.80
Purchase #7	$126.72	11.107%	$140.7948	$140.79	$140.80	$140.80
7 purchase totals =	$591.45		$663.1206	$663.11	$663.10	$663.10