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	$45.56	12.751%	$51.3694	$51.37	$51.35	$51.40
Purchase #2	$111.61	3.350%	$115.3489	$115.35	$115.35	$115.30
Purchase #3	$82.66	9.690%	$90.6698	$90.67	$90.65	$90.70
Purchase #4	$236.90	7.743%	$255.2432	$255.24	$255.25	$255.20
Purchase #5	$33.61	12.445%	$37.7928	$37.79	$37.80	$37.80
Purchase #6	$34.31	5.776%	$36.2917	$36.29	$36.30	$36.30
Purchase #7	$153.83	4.863%	$161.3108	$161.31	$161.30	$161.30
7 purchase totals =	$698.48		$748.0266	$748.02	$748.00	$748.00