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	$81.56	8.639%	$88.606	$88.61	$88.60	$88.60
Purchase #2	$221.90	11.383%	$247.1589	$247.16	$247.15	$247.20
Purchase #3	$242.80	3.553%	$251.4267	$251.43	$251.45	$251.40
Purchase #4	$89.71	12.399%	$100.8331	$100.83	$100.85	$100.80
Purchase #5	$146.51	8.804%	$159.4087	$159.41	$159.40	$159.40
Purchase #6	$31.47	11.843%	$35.197	$35.20	$35.20	$35.20
Purchase #7	$155.91	7.402%	$167.4505	$167.45	$167.45	$167.50
7 purchase totals =	$969.86		$1,050.0809	$1,050.09	$1,050.10	$1,050.10