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	$36.33	13.484%	$41.2287	$41.23	$41.25	$41.20
Purchase #2	$34.48	7.458%	$37.0515	$37.05	$37.05	$37.10
Purchase #3	$80.92	9.152%	$88.3258	$88.33	$88.35	$88.30
Purchase #4	$46.91	10.610%	$51.8872	$51.89	$51.90	$51.90
Purchase #5	$170.36	9.135%	$185.9224	$185.92	$185.90	$185.90
Purchase #6	$145.55	8.488%	$157.9043	$157.90	$157.90	$157.90
Purchase #7	$206.64	8.689%	$224.5949	$224.59	$224.60	$224.60
7 purchase totals =	$721.19		$786.9148	$786.91	$786.95	$786.90