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	$142.61	12.191%	$159.9956	$160.00	$160.00	$160.00
Purchase #2	$25.84	13.448%	$29.315	$29.32	$29.30	$29.30
Purchase #3	$82.34	9.444%	$90.1162	$90.12	$90.10	$90.10
Purchase #4	$106.38	7.228%	$114.0691	$114.07	$114.05	$114.10
Purchase #5	$141.30	10.301%	$155.8553	$155.86	$155.85	$155.90
Purchase #6	$89.95	10.354%	$99.2634	$99.26	$99.25	$99.30
Purchase #7	$198.31	13.381%	$224.8459	$224.85	$224.85	$224.80
7 purchase totals =	$786.73		$873.4605	$873.48	$873.40	$873.50