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	$161.41	4.494%	$168.6638	$168.66	$168.65	$168.70
Purchase #2	$140.30	8.193%	$151.7948	$151.79	$151.80	$151.80
Purchase #3	$30.72	3.439%	$31.7765	$31.78	$31.80	$31.80
Purchase #4	$21.93	7.649%	$23.6074	$23.61	$23.60	$23.60
Purchase #5	$78.33	5.120%	$82.3405	$82.34	$82.35	$82.30
Purchase #6	$25.70	10.363%	$28.3633	$28.36	$28.35	$28.40
Purchase #7	$40.93	10.240%	$45.1212	$45.12	$45.10	$45.10
7 purchase totals =	$499.32		$531.6675	$531.66	$531.65	$531.70