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	$56.88	7.728%	$61.2757	$61.28	$61.30	$61.30
Purchase #2	$100.63	5.131%	$105.7933	$105.79	$105.80	$105.80
Purchase #3	$40.31	13.773%	$45.8619	$45.86	$45.85	$45.90
Purchase #4	$80.34	11.357%	$89.4642	$89.46	$89.45	$89.50
Purchase #5	$6.62	4.728%	$6.933	$6.93	$6.95	$6.90
Purchase #6	$88.55	7.685%	$95.3551	$95.36	$95.35	$95.40
Purchase #7	$243.32	5.407%	$256.4763	$256.48	$256.50	$256.50
7 purchase totals =	$616.65		$661.1595	$661.16	$661.20	$661.30