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	$54.84	6.822%	$58.5812	$58.58	$58.60	$58.60
Purchase #2	$123.85	5.479%	$130.6357	$130.64	$130.65	$130.60
Purchase #3	$59.66	13.170%	$67.5172	$67.52	$67.50	$67.50
Purchase #4	$87.89	3.378%	$90.8589	$90.86	$90.85	$90.90
Purchase #5	$36.50	7.290%	$39.1609	$39.16	$39.15	$39.20
Purchase #6	$148.30	3.166%	$152.9952	$153.00	$153.00	$153.00
Purchase #7	$180.81	4.385%	$188.7385	$188.74	$188.75	$188.70
7 purchase totals =	$691.85		$728.4876	$728.50	$728.50	$728.50