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	$6.57	11.211%	$7.3066	$7.31	$7.30	$7.30
Purchase #2	$243.33	7.767%	$262.2294	$262.23	$262.25	$262.20
Purchase #3	$73.30	13.467%	$83.1713	$83.17	$83.15	$83.20
Purchase #4	$250.93	7.623%	$270.0584	$270.06	$270.05	$270.10
Purchase #5	$214.73	3.800%	$222.8897	$222.89	$222.90	$222.90
Purchase #6	$150.51	6.475%	$160.2555	$160.26	$160.25	$160.30
Purchase #7	$30.49	5.679%	$32.2215	$32.22	$32.20	$32.20
7 purchase totals =	$969.86		$1,038.1324	$1,038.14	$1,038.10	$1,038.20