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	$36.72	3.153%	$37.8778	$37.88	$37.90	$37.90
Purchase #2	$136.96	4.762%	$143.482	$143.48	$143.50	$143.50
Purchase #3	$43.32	9.428%	$47.4042	$47.40	$47.40	$47.40
Purchase #4	$40.39	13.578%	$45.8742	$45.87	$45.85	$45.90
Purchase #5	$124.49	7.521%	$133.8529	$133.85	$133.85	$133.90
Purchase #6	$14.32	10.779%	$15.8636	$15.86	$15.85	$15.90
Purchase #7	$218.85	11.106%	$243.1555	$243.16	$243.15	$243.20
7 purchase totals =	$615.05		$667.5102	$667.50	$667.50	$667.70