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	$28.92	7.872%	$31.1966	$31.20	$31.20	$31.20
Purchase #2	$115.50	6.639%	$123.168	$123.17	$123.15	$123.20
Purchase #3	$165.62	5.708%	$175.0736	$175.07	$175.05	$175.10
Purchase #4	$199.54	8.321%	$216.1437	$216.14	$216.15	$216.10
Purchase #5	$179.40	6.863%	$191.7122	$191.71	$191.70	$191.70
Purchase #6	$33.40	11.620%	$37.2811	$37.28	$37.30	$37.30
Purchase #7	$151.96	13.457%	$172.4093	$172.41	$172.40	$172.40
7 purchase totals =	$874.34		$946.9845	$946.98	$946.95	$947.00