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	$125.25	13.704%	$142.4143	$142.41	$142.40	$142.40
Purchase #2	$246.92	4.176%	$257.2314	$257.23	$257.25	$257.20
Purchase #3	$199.99	10.586%	$221.1609	$221.16	$221.15	$221.20
Purchase #4	$153.31	9.232%	$167.4636	$167.46	$167.45	$167.50
Purchase #5	$178.78	9.373%	$195.537	$195.54	$195.55	$195.50
Purchase #6	$72.35	7.659%	$77.8913	$77.89	$77.90	$77.90
Purchase #7	$241.46	7.507%	$259.5864	$259.59	$259.60	$259.60
7 purchase totals =	$1,218.06		$1,321.2849	$1,321.28	$1,321.30	$1,321.30