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	$6.30	13.743%	$7.1658	$7.17	$7.15	$7.20
Purchase #2	$247.47	10.419%	$273.2539	$273.25	$273.25	$273.30
Purchase #3	$82.58	12.434%	$92.848	$92.85	$92.85	$92.80
Purchase #4	$38.56	5.317%	$40.6102	$40.61	$40.60	$40.60
Purchase #5	$35.56	11.339%	$39.5921	$39.59	$39.60	$39.60
Purchase #6	$85.62	10.166%	$94.3241	$94.32	$94.30	$94.30
Purchase #7	$111.49	10.820%	$123.5532	$123.55	$123.55	$123.60
7 purchase totals =	$607.58		$671.3473	$671.34	$671.30	$671.40