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	$39.66	4.663%	$41.5093	$41.51	$41.50	$41.50
Purchase #2	$232.88	7.485%	$250.3111	$250.31	$250.30	$250.30
Purchase #3	$42.44	5.482%	$44.7666	$44.77	$44.75	$44.80
Purchase #4	$97.60	9.233%	$106.6114	$106.61	$106.60	$106.60
Purchase #5	$95.82	10.145%	$105.5409	$105.54	$105.55	$105.50
Purchase #6	$129.84	8.686%	$141.1179	$141.12	$141.10	$141.10
Purchase #7	$103.39	12.708%	$116.5288	$116.53	$116.55	$116.50
7 purchase totals =	$741.63		$806.3860	$806.39	$806.35	$806.30