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	$151.63	9.760%	$166.4291	$166.43	$166.45	$166.40
Purchase #2	$223.47	8.442%	$242.3353	$242.34	$242.35	$242.30
Purchase #3	$109.39	3.531%	$113.2526	$113.25	$113.25	$113.30
Purchase #4	$125.51	12.763%	$141.5288	$141.53	$141.55	$141.50
Purchase #5	$85.71	8.168%	$92.7108	$92.71	$92.70	$92.70
Purchase #6	$20.54	11.135%	$22.8271	$22.83	$22.85	$22.80
Purchase #7	$65.86	7.644%	$70.8943	$70.89	$70.90	$70.90
7 purchase totals =	$782.11		$849.9780	$849.98	$850.05	$849.90