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	$68.87	6.272%	$73.1895	$73.19	$73.20	$73.20
Purchase #2	$205.97	8.208%	$222.876	$222.88	$222.90	$222.90
Purchase #3	$48.74	3.375%	$50.385	$50.39	$50.40	$50.40
Purchase #4	$89.26	13.664%	$101.4565	$101.46	$101.45	$101.50
Purchase #5	$66.98	6.535%	$71.3571	$71.36	$71.35	$71.40
Purchase #6	$65.65	7.556%	$70.6105	$70.61	$70.60	$70.60
Purchase #7	$63.71	4.470%	$66.5578	$66.56	$66.55	$66.60
7 purchase totals =	$609.18		$656.4324	$656.45	$656.45	$656.60