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	$142.39	6.287%	$151.3421	$151.34	$151.35	$151.30
Purchase #2	$100.59	9.190%	$109.8342	$109.83	$109.85	$109.80
Purchase #3	$119.61	10.466%	$132.1284	$132.13	$132.15	$132.10
Purchase #4	$65.52	3.711%	$67.9514	$67.95	$67.95	$68.00
Purchase #5	$154.28	3.276%	$159.3342	$159.33	$159.35	$159.30
Purchase #6	$36.61	8.778%	$39.8236	$39.82	$39.80	$39.80
Purchase #7	$52.48	6.479%	$55.8802	$55.88	$55.90	$55.90
7 purchase totals =	$671.48		$716.2941	$716.28	$716.35	$716.20