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	$72.63	7.150%	$77.823	$77.82	$77.80	$77.80
Purchase #2	$155.94	11.513%	$173.8934	$173.89	$173.90	$173.90
Purchase #3	$136.51	7.321%	$146.5039	$146.50	$146.50	$146.50
Purchase #4	$104.31	6.423%	$111.0098	$111.01	$111.00	$111.00
Purchase #5	$80.37	7.828%	$86.6614	$86.66	$86.65	$86.70
Purchase #6	$21.48	12.266%	$24.1147	$24.11	$24.10	$24.10
Purchase #7	$15.33	5.620%	$16.1915	$16.19	$16.20	$16.20
7 purchase totals =	$586.57		$636.1977	$636.18	$636.15	$636.20