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	$63.76	4.467%	$66.6082	$66.61	$66.60	$66.60
Purchase #2	$55.77	6.504%	$59.3973	$59.40	$59.40	$59.40
Purchase #3	$126.86	6.122%	$134.6264	$134.63	$134.65	$134.60
Purchase #4	$244.50	11.829%	$273.4219	$273.42	$273.40	$273.40
Purchase #5	$160.76	12.536%	$180.9129	$180.91	$180.90	$180.90
Purchase #6	$6.76	12.268%	$7.5893	$7.59	$7.60	$7.60
Purchase #7	$88.36	7.757%	$95.2141	$95.21	$95.20	$95.20
7 purchase totals =	$746.77		$817.7701	$817.77	$817.75	$817.70