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	$155.56	8.176%	$168.2786	$168.28	$168.30	$168.30
Purchase #2	$238.97	7.472%	$256.8258	$256.83	$256.85	$256.80
Purchase #3	$113.85	8.342%	$123.3474	$123.35	$123.35	$123.30
Purchase #4	$151.59	4.359%	$158.1978	$158.20	$158.20	$158.20
Purchase #5	$227.56	6.860%	$243.1706	$243.17	$243.15	$243.20
Purchase #6	$245.86	9.810%	$269.9789	$269.98	$270.00	$270.00
Purchase #7	$30.88	7.646%	$33.2411	$33.24	$33.25	$33.20
7 purchase totals =	$1,164.27		$1,253.0402	$1,253.05	$1,253.10	$1,253.00