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	$35.45	12.415%	$39.8511	$39.85	$39.85	$39.90
Purchase #2	$13.87	13.699%	$15.7701	$15.77	$15.75	$15.80
Purchase #3	$196.93	7.418%	$211.5383	$211.54	$211.55	$211.50
Purchase #4	$187.46	4.585%	$196.055	$196.06	$196.05	$196.10
Purchase #5	$88.50	12.384%	$99.4598	$99.46	$99.45	$99.50
Purchase #6	$218.83	13.833%	$249.1008	$249.10	$249.10	$249.10
Purchase #7	$226.28	3.477%	$234.1478	$234.15	$234.15	$234.10
7 purchase totals =	$967.32		$1,045.9229	$1,045.93	$1,045.90	$1,046.00