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	$36.28	9.254%	$39.6374	$39.64	$39.65	$39.60
Purchase #2	$14.42	8.483%	$15.6432	$15.64	$15.65	$15.60
Purchase #3	$75.82	9.380%	$82.9319	$82.93	$82.95	$82.90
Purchase #4	$55.42	10.732%	$61.3677	$61.37	$61.35	$61.40
Purchase #5	$196.29	7.447%	$210.9077	$210.91	$210.90	$210.90
Purchase #6	$203.87	10.803%	$225.8941	$225.89	$225.90	$225.90
Purchase #7	$92.88	10.231%	$102.3826	$102.38	$102.40	$102.40
7 purchase totals =	$674.98		$738.7646	$738.76	$738.80	$738.70