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	$25.67	13.414%	$29.1134	$29.11	$29.10	$29.10
Purchase #2	$49.34	8.399%	$53.4841	$53.48	$53.50	$53.50
Purchase #3	$24.82	10.355%	$27.3901	$27.39	$27.40	$27.40
Purchase #4	$189.74	7.649%	$204.2532	$204.25	$204.25	$204.30
Purchase #5	$34.88	8.454%	$37.8288	$37.83	$37.85	$37.80
Purchase #6	$90.29	11.776%	$100.9226	$100.92	$100.90	$100.90
Purchase #7	$203.43	6.262%	$216.1688	$216.17	$216.15	$216.20
7 purchase totals =	$618.17		$669.1610	$669.15	$669.15	$669.20