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	$203.70	4.182%	$212.2187	$212.22	$212.20	$212.20
Purchase #2	$109.80	6.680%	$117.1346	$117.13	$117.15	$117.10
Purchase #3	$86.76	3.541%	$89.8322	$89.83	$89.85	$89.80
Purchase #4	$40.70	7.140%	$43.606	$43.61	$43.60	$43.60
Purchase #5	$73.72	5.725%	$77.9405	$77.94	$77.95	$77.90
Purchase #6	$60.87	13.544%	$69.1142	$69.11	$69.10	$69.10
Purchase #7	$162.95	5.234%	$171.4788	$171.48	$171.50	$171.50
7 purchase totals =	$738.50		$781.3250	$781.32	$781.35	$781.20