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	$250.34	3.813%	$259.8855	$259.89	$259.90	$259.90
Purchase #2	$76.88	11.119%	$85.4283	$85.43	$85.45	$85.40
Purchase #3	$51.30	10.177%	$56.5208	$56.52	$56.50	$56.50
Purchase #4	$113.25	8.559%	$122.9431	$122.94	$122.95	$122.90
Purchase #5	$53.73	12.801%	$60.608	$60.61	$60.60	$60.60
Purchase #6	$137.45	9.834%	$150.9668	$150.97	$150.95	$151.00
Purchase #7	$213.42	11.126%	$237.1651	$237.17	$237.15	$237.20
7 purchase totals =	$896.37		$973.5176	$973.53	$973.50	$973.50