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	$136.44	8.327%	$147.8014	$147.80	$147.80	$147.80
Purchase #2	$193.30	12.188%	$216.8594	$216.86	$216.85	$216.90
Purchase #3	$160.98	9.847%	$176.8317	$176.83	$176.85	$176.80
Purchase #4	$172.37	6.686%	$183.8947	$183.89	$183.90	$183.90
Purchase #5	$209.91	5.369%	$221.1801	$221.18	$221.20	$221.20
Purchase #6	$65.89	8.168%	$71.2719	$71.27	$71.25	$71.30
Purchase #7	$95.62	5.573%	$100.9489	$100.95	$100.95	$100.90
7 purchase totals =	$1,034.51		$1,118.7881	$1,118.78	$1,118.80	$1,118.80