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	$34.72	8.853%	$37.7938	$37.79	$37.80	$37.80
Purchase #2	$21.46	3.165%	$22.1392	$22.14	$22.15	$22.10
Purchase #3	$52.87	12.607%	$59.5353	$59.54	$59.55	$59.50
Purchase #4	$238.51	5.227%	$250.9769	$250.98	$251.00	$251.00
Purchase #5	$90.99	7.848%	$98.1309	$98.13	$98.15	$98.10
Purchase #6	$208.91	7.111%	$223.7656	$223.77	$223.75	$223.80
Purchase #7	$123.49	13.555%	$140.2291	$140.23	$140.25	$140.20
7 purchase totals =	$770.95		$832.5708	$832.58	$832.65	$832.50