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	$159.73	12.494%	$179.6867	$179.69	$179.70	$179.70
Purchase #2	$146.69	7.432%	$157.592	$157.59	$157.60	$157.60
Purchase #3	$41.86	8.712%	$45.5068	$45.51	$45.50	$45.50
Purchase #4	$40.29	11.705%	$45.0059	$45.01	$45.00	$45.00
Purchase #5	$42.80	13.345%	$48.5117	$48.51	$48.50	$48.50
Purchase #6	$35.40	4.870%	$37.124	$37.12	$37.10	$37.10
Purchase #7	$212.66	9.449%	$232.7542	$232.75	$232.75	$232.80
7 purchase totals =	$679.43		$746.1813	$746.18	$746.15	$746.20