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	$178.67	7.251%	$191.6254	$191.63	$191.65	$191.60
Purchase #2	$145.47	4.651%	$152.2358	$152.24	$152.25	$152.20
Purchase #3	$29.87	4.334%	$31.1646	$31.16	$31.15	$31.20
Purchase #4	$78.99	11.223%	$87.855	$87.86	$87.85	$87.90
Purchase #5	$141.94	5.441%	$149.663	$149.66	$149.65	$149.70
Purchase #6	$37.29	9.505%	$40.8344	$40.83	$40.85	$40.80
Purchase #7	$146.29	10.764%	$162.0367	$162.04	$162.05	$162.00
7 purchase totals =	$758.52		$815.4149	$815.42	$815.45	$815.40