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	$29.55	7.192%	$31.6752	$31.68	$31.70	$31.70
Purchase #2	$6.77	3.821%	$7.0287	$7.03	$7.05	$7.00
Purchase #3	$119.42	10.433%	$131.8791	$131.88	$131.90	$131.90
Purchase #4	$68.92	12.518%	$77.5474	$77.55	$77.55	$77.50
Purchase #5	$30.97	5.465%	$32.6625	$32.66	$32.65	$32.70
Purchase #6	$220.89	12.321%	$248.1059	$248.11	$248.10	$248.10
Purchase #7	$54.29	12.633%	$61.1485	$61.15	$61.15	$61.10
7 purchase totals =	$530.81		$590.0473	$590.06	$590.10	$590.00