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	$53.83	3.314%	$55.6139	$55.61	$55.60	$55.60
Purchase #2	$54.73	12.140%	$61.3742	$61.37	$61.35	$61.40
Purchase #3	$118.38	13.111%	$133.9008	$133.90	$133.90	$133.90
Purchase #4	$48.28	8.153%	$52.2163	$52.22	$52.20	$52.20
Purchase #5	$116.75	6.843%	$124.7392	$124.74	$124.75	$124.70
Purchase #6	$147.56	3.615%	$152.8943	$152.89	$152.90	$152.90
Purchase #7	$63.55	7.316%	$68.1993	$68.20	$68.20	$68.20
7 purchase totals =	$603.08		$648.9380	$648.93	$648.90	$648.90