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	$236.44	4.562%	$247.2264	$247.23	$247.25	$247.20
Purchase #2	$36.52	8.794%	$39.7316	$39.73	$39.75	$39.70
Purchase #3	$86.78	3.239%	$89.5908	$89.59	$89.60	$89.60
Purchase #4	$125.82	4.195%	$131.0981	$131.10	$131.10	$131.10
Purchase #5	$151.53	11.213%	$168.5211	$168.52	$168.50	$168.50
Purchase #6	$34.92	8.376%	$37.8449	$37.84	$37.85	$37.80
Purchase #7	$164.53	9.593%	$180.3134	$180.31	$180.30	$180.30
7 purchase totals =	$836.54		$894.3263	$894.32	$894.35	$894.20