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	$19.64	6.619%	$20.94	$20.94	$20.95	$20.90
Purchase #2	$56.38	7.465%	$60.5888	$60.59	$60.60	$60.60
Purchase #3	$250.86	8.791%	$272.9131	$272.91	$272.90	$272.90
Purchase #4	$155.46	10.251%	$171.3962	$171.40	$171.40	$171.40
Purchase #5	$141.66	7.134%	$151.766	$151.77	$151.75	$151.80
Purchase #6	$18.89	5.688%	$19.9645	$19.96	$19.95	$20.00
Purchase #7	$54.50	9.835%	$59.8601	$59.86	$59.85	$59.90
7 purchase totals =	$697.39		$757.4287	$757.43	$757.40	$757.50