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	$19.28	4.806%	$20.2066	$20.21	$20.20	$20.20
Purchase #2	$221.88	5.451%	$233.9747	$233.97	$233.95	$234.00
Purchase #3	$74.59	5.202%	$78.4702	$78.47	$78.45	$78.50
Purchase #4	$29.71	13.799%	$33.8097	$33.81	$33.80	$33.80
Purchase #5	$143.97	6.133%	$152.7997	$152.80	$152.80	$152.80
Purchase #6	$126.39	11.140%	$140.4698	$140.47	$140.45	$140.50
Purchase #7	$6.41	12.842%	$7.2332	$7.23	$7.25	$7.20
7 purchase totals =	$622.23		$666.9639	$666.96	$666.90	$667.00