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	$246.63	4.849%	$258.5891	$258.59	$258.60	$258.60
Purchase #2	$120.72	13.146%	$136.5899	$136.59	$136.60	$136.60
Purchase #3	$230.25	11.427%	$256.5607	$256.56	$256.55	$256.60
Purchase #4	$130.61	8.551%	$141.7785	$141.78	$141.80	$141.80
Purchase #5	$7.79	11.544%	$8.6893	$8.69	$8.70	$8.70
Purchase #6	$170.66	5.127%	$179.4097	$179.41	$179.40	$179.40
Purchase #7	$116.75	5.388%	$123.0405	$123.04	$123.05	$123.00
7 purchase totals =	$1,023.41		$1,104.6577	$1,104.66	$1,104.70	$1,104.70