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	$15.47	11.829%	$17.2999	$17.30	$17.30	$17.30
Purchase #2	$201.30	12.192%	$225.8425	$225.84	$225.85	$225.80
Purchase #3	$244.79	4.444%	$255.6685	$255.67	$255.65	$255.70
Purchase #4	$35.33	11.314%	$39.3272	$39.33	$39.35	$39.30
Purchase #5	$241.52	11.577%	$269.4808	$269.48	$269.50	$269.50
Purchase #6	$226.25	10.832%	$250.7574	$250.76	$250.75	$250.80
Purchase #7	$225.94	7.206%	$242.2212	$242.22	$242.20	$242.20
7 purchase totals =	$1,190.60		$1,300.5975	$1,300.60	$1,300.60	$1,300.60