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	$116.59	13.225%	$132.009	$132.01	$132.00	$132.00
Purchase #2	$107.67	4.852%	$112.8941	$112.89	$112.90	$112.90
Purchase #3	$45.46	12.231%	$51.0202	$51.02	$51.00	$51.00
Purchase #4	$182.41	13.352%	$206.7654	$206.77	$206.75	$206.80
Purchase #5	$82.31	11.622%	$91.8761	$91.88	$91.90	$91.90
Purchase #6	$156.35	10.193%	$172.2868	$172.29	$172.30	$172.30
Purchase #7	$49.73	6.314%	$52.87	$52.87	$52.85	$52.90
7 purchase totals =	$740.52		$819.7216	$819.73	$819.70	$819.80