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	$232.42	13.374%	$263.5039	$263.50	$263.50	$263.50
Purchase #2	$83.36	6.865%	$89.0827	$89.08	$89.10	$89.10
Purchase #3	$56.46	10.593%	$62.4408	$62.44	$62.45	$62.40
Purchase #4	$40.37	4.266%	$42.0922	$42.09	$42.10	$42.10
Purchase #5	$135.70	12.435%	$152.5743	$152.57	$152.55	$152.60
Purchase #6	$108.88	3.380%	$112.5601	$112.56	$112.55	$112.60
Purchase #7	$165.76	8.359%	$179.6159	$179.62	$179.60	$179.60
7 purchase totals =	$822.95		$901.8699	$901.86	$901.85	$901.90