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	$123.49	7.493%	$132.7431	$132.74	$132.75	$132.70
Purchase #2	$240.44	6.184%	$255.3088	$255.31	$255.30	$255.30
Purchase #3	$132.66	10.272%	$146.2868	$146.29	$146.30	$146.30
Purchase #4	$73.40	13.624%	$83.4	$83.40	$83.40	$83.40
Purchase #5	$225.57	8.600%	$244.969	$244.97	$244.95	$245.00
Purchase #6	$185.25	3.537%	$191.8023	$191.80	$191.80	$191.80
Purchase #7	$69.59	13.405%	$78.9185	$78.92	$78.90	$78.90
7 purchase totals =	$1,050.40		$1,133.4285	$1,133.43	$1,133.40	$1,133.40