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	$71.78	6.541%	$76.4751	$76.48	$76.50	$76.50
Purchase #2	$244.85	6.155%	$259.9205	$259.92	$259.90	$259.90
Purchase #3	$38.37	10.538%	$42.4134	$42.41	$42.40	$42.40
Purchase #4	$138.67	11.298%	$154.3369	$154.34	$154.35	$154.30
Purchase #5	$50.89	8.854%	$55.3958	$55.40	$55.40	$55.40
Purchase #6	$108.68	5.437%	$114.5889	$114.59	$114.60	$114.60
Purchase #7	$114.64	3.290%	$118.4117	$118.41	$118.40	$118.40
7 purchase totals =	$767.88		$821.5423	$821.55	$821.55	$821.50