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	$147.31	12.314%	$165.4498	$165.45	$165.45	$165.40
Purchase #2	$40.94	12.203%	$45.9359	$45.94	$45.95	$45.90
Purchase #3	$30.25	8.852%	$32.9277	$32.93	$32.95	$32.90
Purchase #4	$42.51	9.734%	$46.6479	$46.65	$46.65	$46.60
Purchase #5	$246.82	11.390%	$274.9328	$274.93	$274.95	$274.90
Purchase #6	$11.34	9.705%	$12.4405	$12.44	$12.45	$12.40
Purchase #7	$76.92	12.386%	$86.4473	$86.45	$86.45	$86.40
7 purchase totals =	$596.09		$664.7819	$664.79	$664.85	$664.50