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	$16.56	9.294%	$18.0991	$18.10	$18.10	$18.10
Purchase #2	$32.71	5.614%	$34.5463	$34.55	$34.55	$34.50
Purchase #3	$186.34	5.402%	$196.4061	$196.41	$196.40	$196.40
Purchase #4	$139.74	4.461%	$145.9738	$145.97	$145.95	$146.00
Purchase #5	$156.46	11.139%	$173.8881	$173.89	$173.90	$173.90
Purchase #6	$152.78	4.512%	$159.6734	$159.67	$159.65	$159.70
Purchase #7	$155.45	10.558%	$171.8624	$171.86	$171.85	$171.90
7 purchase totals =	$840.04		$900.4492	$900.45	$900.40	$900.50