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	$139.34	4.146%	$145.117	$145.12	$145.10	$145.10
Purchase #2	$131.44	7.221%	$140.9313	$140.93	$140.95	$140.90
Purchase #3	$74.82	10.500%	$82.6761	$82.68	$82.70	$82.70
Purchase #4	$250.60	9.501%	$274.4095	$274.41	$274.40	$274.40
Purchase #5	$99.89	4.142%	$104.0274	$104.03	$104.05	$104.00
Purchase #6	$77.58	6.137%	$82.3411	$82.34	$82.35	$82.30
Purchase #7	$51.82	13.604%	$58.8696	$58.87	$58.85	$58.90
7 purchase totals =	$825.49		$888.3720	$888.38	$888.40	$888.30