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	$31.30	5.750%	$33.0998	$33.10	$33.10	$33.10
Purchase #2	$155.63	13.181%	$176.1436	$176.14	$176.15	$176.10
Purchase #3	$13.46	12.614%	$15.1578	$15.16	$15.15	$15.20
Purchase #4	$77.94	6.112%	$82.7037	$82.70	$82.70	$82.70
Purchase #5	$132.32	10.791%	$146.5987	$146.60	$146.60	$146.60
Purchase #6	$108.75	13.272%	$123.1833	$123.18	$123.20	$123.20
Purchase #7	$95.63	11.221%	$106.3606	$106.36	$106.35	$106.40
7 purchase totals =	$615.03		$683.2475	$683.24	$683.25	$683.30