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	$64.79	8.653%	$70.3963	$70.40	$70.40	$70.40
Purchase #2	$37.71	11.709%	$42.1255	$42.13	$42.15	$42.10
Purchase #3	$157.94	6.245%	$167.8034	$167.80	$167.80	$167.80
Purchase #4	$73.59	13.317%	$83.39	$83.39	$83.40	$83.40
Purchase #5	$48.92	3.868%	$50.8122	$50.81	$50.80	$50.80
Purchase #6	$154.50	13.274%	$175.0083	$175.01	$175.00	$175.00
Purchase #7	$19.37	5.264%	$20.3896	$20.39	$20.40	$20.40
7 purchase totals =	$556.82		$609.9253	$609.93	$609.95	$609.90