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	$78.59	5.731%	$83.094	$83.09	$83.10	$83.10
Purchase #2	$129.82	9.496%	$142.1477	$142.15	$142.15	$142.10
Purchase #3	$222.52	6.475%	$236.9282	$236.93	$236.95	$236.90
Purchase #4	$31.85	13.463%	$36.138	$36.14	$36.15	$36.10
Purchase #5	$36.30	8.282%	$39.3064	$39.31	$39.30	$39.30
Purchase #6	$138.37	9.306%	$151.2467	$151.25	$151.25	$151.20
Purchase #7	$198.84	7.738%	$214.2262	$214.23	$214.25	$214.20
7 purchase totals =	$836.29		$903.0872	$903.10	$903.15	$902.90