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	$121.25	8.146%	$131.127	$131.13	$131.15	$131.10
Purchase #2	$160.26	9.645%	$175.7171	$175.72	$175.70	$175.70
Purchase #3	$72.43	12.242%	$81.2969	$81.30	$81.30	$81.30
Purchase #4	$239.70	13.796%	$272.769	$272.77	$272.75	$272.80
Purchase #5	$231.46	12.778%	$261.036	$261.04	$261.05	$261.00
Purchase #6	$111.60	4.624%	$116.7604	$116.76	$116.75	$116.80
Purchase #7	$83.32	11.275%	$92.7143	$92.71	$92.70	$92.70
7 purchase totals =	$1,020.02		$1,131.4207	$1,131.43	$1,131.40	$1,131.40