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	$152.58	12.224%	$171.2314	$171.23	$171.25	$171.20
Purchase #2	$224.96	4.331%	$234.703	$234.70	$234.70	$234.70
Purchase #3	$12.84	12.284%	$14.4173	$14.42	$14.40	$14.40
Purchase #4	$228.66	12.332%	$256.8584	$256.86	$256.85	$256.90
Purchase #5	$55.94	12.134%	$62.7278	$62.73	$62.75	$62.70
Purchase #6	$89.31	12.333%	$100.3246	$100.32	$100.30	$100.30
Purchase #7	$75.93	13.325%	$86.0477	$86.05	$86.05	$86.00
7 purchase totals =	$840.22		$926.3102	$926.31	$926.30	$926.20