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	$244.54	12.270%	$274.5451	$274.55	$274.55	$274.50
Purchase #2	$122.89	11.511%	$137.0359	$137.04	$137.05	$137.00
Purchase #3	$130.57	5.105%	$137.2356	$137.24	$137.25	$137.20
Purchase #4	$148.30	5.342%	$156.2222	$156.22	$156.20	$156.20
Purchase #5	$150.95	10.203%	$166.3514	$166.35	$166.35	$166.40
Purchase #6	$50.42	4.218%	$52.5467	$52.55	$52.55	$52.50
Purchase #7	$31.88	3.240%	$32.9129	$32.91	$32.90	$32.90
7 purchase totals =	$879.55		$956.8498	$956.86	$956.85	$956.70