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	$170.74	11.350%	$190.119	$190.12	$190.10	$190.10
Purchase #2	$121.49	5.325%	$127.9593	$127.96	$127.95	$128.00
Purchase #3	$46.89	5.586%	$49.5093	$49.51	$49.50	$49.50
Purchase #4	$73.91	5.663%	$78.0955	$78.10	$78.10	$78.10
Purchase #5	$161.29	4.523%	$168.5851	$168.59	$168.60	$168.60
Purchase #6	$52.51	10.754%	$58.1569	$58.16	$58.15	$58.20
Purchase #7	$14.84	13.854%	$16.8959	$16.90	$16.90	$16.90
7 purchase totals =	$641.67		$689.3210	$689.34	$689.30	$689.40