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	$47.50	13.190%	$53.7653	$53.77	$53.75	$53.80
Purchase #2	$45.73	12.818%	$51.5917	$51.59	$51.60	$51.60
Purchase #3	$124.26	13.486%	$141.0177	$141.02	$141.00	$141.00
Purchase #4	$108.29	8.247%	$117.2207	$117.22	$117.20	$117.20
Purchase #5	$30.65	9.152%	$33.4551	$33.46	$33.45	$33.50
Purchase #6	$89.72	9.553%	$98.291	$98.29	$98.30	$98.30
Purchase #7	$104.79	11.377%	$116.712	$116.71	$116.70	$116.70
7 purchase totals =	$550.94		$612.0535	$612.06	$612.00	$612.10