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	$194.52	11.329%	$216.5572	$216.56	$216.55	$216.60
Purchase #2	$156.40	11.265%	$174.0185	$174.02	$174.00	$174.00
Purchase #3	$217.70	13.406%	$246.8849	$246.88	$246.90	$246.90
Purchase #4	$12.98	3.831%	$13.4773	$13.48	$13.50	$13.50
Purchase #5	$38.89	10.145%	$42.8354	$42.84	$42.85	$42.80
Purchase #6	$42.41	8.311%	$45.9347	$45.93	$45.95	$45.90
Purchase #7	$57.78	13.625%	$65.6525	$65.65	$65.65	$65.70
7 purchase totals =	$720.68		$805.3605	$805.36	$805.40	$805.40