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	$29.47	8.168%	$31.8771	$31.88	$31.90	$31.90
Purchase #2	$138.44	12.481%	$155.7187	$155.72	$155.70	$155.70
Purchase #3	$137.63	9.321%	$150.4585	$150.46	$150.45	$150.50
Purchase #4	$37.43	6.134%	$39.726	$39.73	$39.75	$39.70
Purchase #5	$14.48	9.328%	$15.8307	$15.83	$15.85	$15.80
Purchase #6	$111.30	4.335%	$116.1249	$116.12	$116.10	$116.10
Purchase #7	$142.49	10.664%	$157.6851	$157.69	$157.70	$157.70
7 purchase totals =	$611.24		$667.4210	$667.43	$667.45	$667.40