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	$70.54	7.373%	$75.7409	$75.74	$75.75	$75.70
Purchase #2	$35.32	6.788%	$37.7175	$37.72	$37.70	$37.70
Purchase #3	$98.90	13.123%	$111.8786	$111.88	$111.90	$111.90
Purchase #4	$213.62	8.410%	$231.5854	$231.59	$231.60	$231.60
Purchase #5	$48.69	6.855%	$52.0277	$52.03	$52.05	$52.00
Purchase #6	$33.98	10.662%	$37.6029	$37.60	$37.60	$37.60
Purchase #7	$87.44	3.114%	$90.1629	$90.16	$90.15	$90.20
7 purchase totals =	$588.49		$636.7159	$636.72	$636.75	$636.70