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	$201.77	10.473%	$222.9014	$222.90	$222.90	$222.90
Purchase #2	$168.52	13.287%	$190.9113	$190.91	$190.90	$190.90
Purchase #3	$28.95	13.209%	$32.774	$32.77	$32.75	$32.80
Purchase #4	$110.98	5.107%	$116.6477	$116.65	$116.65	$116.60
Purchase #5	$73.91	13.493%	$83.8827	$83.88	$83.90	$83.90
Purchase #6	$106.41	10.226%	$117.2915	$117.29	$117.30	$117.30
Purchase #7	$144.88	7.213%	$155.3302	$155.33	$155.35	$155.30
7 purchase totals =	$835.42		$919.7388	$919.73	$919.75	$919.70