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	$7.44	3.854%	$7.7267	$7.73	$7.75	$7.70
Purchase #2	$94.71	11.697%	$105.7882	$105.79	$105.80	$105.80
Purchase #3	$246.93	13.727%	$280.8261	$280.83	$280.85	$280.80
Purchase #4	$180.61	5.195%	$189.9927	$189.99	$190.00	$190.00
Purchase #5	$240.69	7.123%	$257.8343	$257.83	$257.85	$257.80
Purchase #6	$67.90	5.717%	$71.7818	$71.78	$71.80	$71.80
Purchase #7	$166.51	12.752%	$187.7434	$187.74	$187.75	$187.70
7 purchase totals =	$1,004.79		$1,101.6932	$1,101.69	$1,101.80	$1,101.60