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	$21.46	4.429%	$22.4105	$22.41	$22.40	$22.40
Purchase #2	$165.37	13.874%	$188.3134	$188.31	$188.30	$188.30
Purchase #3	$16.42	10.755%	$18.186	$18.19	$18.20	$18.20
Purchase #4	$161.25	3.730%	$167.2646	$167.26	$167.25	$167.30
Purchase #5	$31.87	11.756%	$35.6166	$35.62	$35.60	$35.60
Purchase #6	$67.58	6.439%	$71.9315	$71.93	$71.95	$71.90
Purchase #7	$164.46	10.413%	$181.5852	$181.59	$181.60	$181.60
7 purchase totals =	$628.41		$685.3078	$685.31	$685.30	$685.30