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	$238.59	6.385%	$253.824	$253.82	$253.80	$253.80
Purchase #2	$115.41	10.567%	$127.6054	$127.61	$127.60	$127.60
Purchase #3	$22.94	8.448%	$24.878	$24.88	$24.90	$24.90
Purchase #4	$200.78	10.759%	$222.3819	$222.38	$222.40	$222.40
Purchase #5	$142.66	9.256%	$155.8646	$155.86	$155.85	$155.90
Purchase #6	$95.91	11.155%	$106.6088	$106.61	$106.60	$106.60
Purchase #7	$250.63	11.318%	$278.9963	$279.00	$279.00	$279.00
7 purchase totals =	$1,066.92		$1,170.1590	$1,170.16	$1,170.15	$1,170.20