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	$63.78	13.666%	$72.4962	$72.50	$72.50	$72.50
Purchase #2	$214.83	3.801%	$222.9957	$223.00	$223.00	$223.00
Purchase #3	$75.29	8.366%	$81.5888	$81.59	$81.60	$81.60
Purchase #4	$89.41	10.636%	$98.9196	$98.92	$98.90	$98.90
Purchase #5	$112.85	5.353%	$118.8909	$118.89	$118.90	$118.90
Purchase #6	$92.37	6.358%	$98.2429	$98.24	$98.25	$98.20
Purchase #7	$28.78	3.263%	$29.7191	$29.72	$29.70	$29.70
7 purchase totals =	$677.31		$722.8532	$722.86	$722.85	$722.80