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	$38.89	11.485%	$43.3565	$43.36	$43.35	$43.40
Purchase #2	$142.87	3.485%	$147.849	$147.85	$147.85	$147.80
Purchase #3	$128.90	13.853%	$146.7565	$146.76	$146.75	$146.80
Purchase #4	$193.56	9.117%	$211.2069	$211.21	$211.20	$211.20
Purchase #5	$139.54	9.546%	$152.8605	$152.86	$152.85	$152.90
Purchase #6	$81.37	7.188%	$87.2189	$87.22	$87.20	$87.20
Purchase #7	$173.65	6.642%	$185.1838	$185.18	$185.20	$185.20
7 purchase totals =	$898.78		$974.4321	$974.44	$974.40	$974.50