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	$80.78	11.465%	$90.0414	$90.04	$90.05	$90.00
Purchase #2	$174.86	13.543%	$198.5413	$198.54	$198.55	$198.50
Purchase #3	$146.98	4.672%	$153.8469	$153.85	$153.85	$153.80
Purchase #4	$19.62	13.639%	$22.296	$22.30	$22.30	$22.30
Purchase #5	$241.56	13.571%	$274.3421	$274.34	$274.35	$274.30
Purchase #6	$103.89	10.145%	$114.4296	$114.43	$114.45	$114.40
Purchase #7	$184.30	13.540%	$209.2542	$209.25	$209.25	$209.30
7 purchase totals =	$951.99		$1,062.7515	$1,062.75	$1,062.80	$1,062.60