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	$92.91	8.117%	$100.4515	$100.45	$100.45	$100.50
Purchase #2	$132.52	13.484%	$150.389	$150.39	$150.40	$150.40
Purchase #3	$83.96	11.328%	$93.471	$93.47	$93.45	$93.50
Purchase #4	$45.98	8.850%	$50.0492	$50.05	$50.05	$50.00
Purchase #5	$202.81	7.282%	$217.5786	$217.58	$217.60	$217.60
Purchase #6	$238.42	12.759%	$268.84	$268.84	$268.85	$268.80
Purchase #7	$154.94	9.667%	$169.918	$169.92	$169.90	$169.90
7 purchase totals =	$951.54		$1,050.6973	$1,050.70	$1,050.70	$1,050.70