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	$48.61	12.844%	$54.8535	$54.85	$54.85	$54.90
Purchase #2	$150.53	4.515%	$157.3264	$157.33	$157.35	$157.30
Purchase #3	$31.57	6.398%	$33.5898	$33.59	$33.60	$33.60
Purchase #4	$151.69	13.504%	$172.1742	$172.17	$172.15	$172.20
Purchase #5	$207.34	4.200%	$216.0483	$216.05	$216.05	$216.00
Purchase #6	$11.71	9.642%	$12.8391	$12.84	$12.85	$12.80
Purchase #7	$12.76	8.274%	$13.8158	$13.82	$13.80	$13.80
7 purchase totals =	$614.21		$660.6471	$660.65	$660.65	$660.60