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	$246.29	4.414%	$257.1612	$257.16	$257.15	$257.20
Purchase #2	$166.92	3.339%	$172.4935	$172.49	$172.50	$172.50
Purchase #3	$139.87	5.443%	$147.4831	$147.48	$147.50	$147.50
Purchase #4	$49.58	12.837%	$55.9446	$55.94	$55.95	$55.90
Purchase #5	$19.40	9.331%	$21.2102	$21.21	$21.20	$21.20
Purchase #6	$92.69	6.707%	$98.9067	$98.91	$98.90	$98.90
Purchase #7	$235.73	8.269%	$255.2225	$255.22	$255.20	$255.20
7 purchase totals =	$950.48		$1,008.4218	$1,008.41	$1,008.40	$1,008.40