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	$57.39	6.570%	$61.1605	$61.16	$61.15	$61.20
Purchase #2	$39.80	7.444%	$42.7627	$42.76	$42.75	$42.80
Purchase #3	$136.34	4.321%	$142.2313	$142.23	$142.25	$142.20
Purchase #4	$80.59	13.131%	$91.1723	$91.17	$91.15	$91.20
Purchase #5	$110.33	5.196%	$116.0627	$116.06	$116.05	$116.10
Purchase #6	$78.87	4.366%	$82.3135	$82.31	$82.30	$82.30
Purchase #7	$29.28	13.595%	$33.2606	$33.26	$33.25	$33.30
7 purchase totals =	$532.60		$568.9636	$568.95	$568.90	$569.10