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	$28.29	9.274%	$30.9136	$30.91	$30.90	$30.90
Purchase #2	$36.27	8.709%	$39.4288	$39.43	$39.45	$39.40
Purchase #3	$29.93	3.636%	$31.0183	$31.02	$31.00	$31.00
Purchase #4	$153.72	11.456%	$171.3302	$171.33	$171.35	$171.30
Purchase #5	$32.68	12.669%	$36.8202	$36.82	$36.80	$36.80
Purchase #6	$173.59	10.112%	$191.1434	$191.14	$191.15	$191.10
Purchase #7	$100.57	4.572%	$105.1681	$105.17	$105.15	$105.20
7 purchase totals =	$555.05		$605.8226	$605.82	$605.80	$605.70