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	$7.92	8.514%	$8.5943	$8.59	$8.60	$8.60
Purchase #2	$50.72	8.323%	$54.9414	$54.94	$54.95	$54.90
Purchase #3	$222.82	11.756%	$249.0147	$249.01	$249.00	$249.00
Purchase #4	$190.49	9.647%	$208.8666	$208.87	$208.85	$208.90
Purchase #5	$102.84	8.867%	$111.9588	$111.96	$111.95	$112.00
Purchase #6	$180.35	9.110%	$196.7799	$196.78	$196.80	$196.80
Purchase #7	$50.43	6.780%	$53.8492	$53.85	$53.85	$53.80
7 purchase totals =	$805.57		$884.0049	$884.00	$884.00	$884.00