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	$84.31	7.217%	$90.3947	$90.39	$90.40	$90.40
Purchase #2	$120.61	8.445%	$130.7955	$130.80	$130.80	$130.80
Purchase #3	$124.97	10.310%	$137.8544	$137.85	$137.85	$137.90
Purchase #4	$179.29	6.278%	$190.5458	$190.55	$190.55	$190.50
Purchase #5	$57.34	12.378%	$64.4375	$64.44	$64.45	$64.40
Purchase #6	$201.72	10.436%	$222.7715	$222.77	$222.75	$222.80
Purchase #7	$201.69	13.647%	$229.2146	$229.21	$229.20	$229.20
7 purchase totals =	$969.93		$1,066.0140	$1,066.01	$1,066.00	$1,066.00