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	$18.83	8.185%	$20.3712	$20.37	$20.35	$20.40
Purchase #2	$126.48	11.838%	$141.4527	$141.45	$141.45	$141.50
Purchase #3	$67.81	5.299%	$71.4033	$71.40	$71.40	$71.40
Purchase #4	$146.79	12.783%	$165.5542	$165.55	$165.55	$165.60
Purchase #5	$17.59	12.318%	$19.7567	$19.76	$19.75	$19.80
Purchase #6	$131.89	6.735%	$140.7728	$140.77	$140.75	$140.80
Purchase #7	$159.40	5.615%	$168.3503	$168.35	$168.35	$168.40
7 purchase totals =	$668.79		$727.6612	$727.65	$727.60	$727.90