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	$207.41	11.567%	$231.4011	$231.40	$231.40	$231.40
Purchase #2	$192.63	6.828%	$205.7828	$205.78	$205.80	$205.80
Purchase #3	$139.80	12.130%	$156.7577	$156.76	$156.75	$156.80
Purchase #4	$67.48	13.842%	$76.8206	$76.82	$76.80	$76.80
Purchase #5	$82.71	13.833%	$94.1513	$94.15	$94.15	$94.20
Purchase #6	$35.37	5.687%	$37.3815	$37.38	$37.40	$37.40
Purchase #7	$208.27	9.365%	$227.7745	$227.77	$227.75	$227.80
7 purchase totals =	$933.67		$1,030.0695	$1,030.06	$1,030.05	$1,030.20