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	$235.97	7.800%	$254.3757	$254.38	$254.40	$254.40
Purchase #2	$125.40	6.712%	$133.8168	$133.82	$133.80	$133.80
Purchase #3	$172.28	4.757%	$180.4754	$180.48	$180.50	$180.50
Purchase #4	$54.60	4.724%	$57.1793	$57.18	$57.20	$57.20
Purchase #5	$211.58	7.440%	$227.3216	$227.32	$227.30	$227.30
Purchase #6	$86.78	13.166%	$98.2055	$98.21	$98.20	$98.20
Purchase #7	$190.70	3.181%	$196.7662	$196.77	$196.75	$196.80
7 purchase totals =	$1,077.31		$1,148.1405	$1,148.16	$1,148.15	$1,148.20