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	$44.39	11.183%	$49.3541	$49.35	$49.35	$49.40
Purchase #2	$137.99	9.796%	$151.5075	$151.51	$151.50	$151.50
Purchase #3	$94.84	10.409%	$104.7119	$104.71	$104.70	$104.70
Purchase #4	$137.63	7.234%	$147.5862	$147.59	$147.60	$147.60
Purchase #5	$134.33	9.683%	$147.3372	$147.34	$147.35	$147.30
Purchase #6	$25.94	12.307%	$29.1324	$29.13	$29.15	$29.10
Purchase #7	$35.98	3.872%	$37.3731	$37.37	$37.35	$37.40
7 purchase totals =	$611.10		$667.0024	$667.00	$667.00	$667.00