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	$72.61	4.556%	$75.9181	$75.92	$75.90	$75.90
Purchase #2	$99.89	11.137%	$111.0147	$111.01	$111.00	$111.00
Purchase #3	$28.83	13.448%	$32.7071	$32.71	$32.70	$32.70
Purchase #4	$209.35	7.329%	$224.6933	$224.69	$224.70	$224.70
Purchase #5	$105.43	5.537%	$111.2677	$111.27	$111.25	$111.30
Purchase #6	$104.51	11.569%	$116.6008	$116.60	$116.60	$116.60
Purchase #7	$27.54	12.444%	$30.9671	$30.97	$30.95	$31.00
7 purchase totals =	$648.16		$703.1688	$703.17	$703.10	$703.20