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	$88.53	13.825%	$100.7693	$100.77	$100.75	$100.80
Purchase #2	$87.33	4.788%	$91.5114	$91.51	$91.50	$91.50
Purchase #3	$107.56	8.630%	$116.8424	$116.84	$116.85	$116.80
Purchase #4	$74.88	11.376%	$83.3983	$83.40	$83.40	$83.40
Purchase #5	$69.57	12.677%	$78.3894	$78.39	$78.40	$78.40
Purchase #6	$27.39	5.360%	$28.8581	$28.86	$28.85	$28.90
Purchase #7	$249.62	6.870%	$266.7689	$266.77	$266.75	$266.80
7 purchase totals =	$704.88		$766.5378	$766.54	$766.50	$766.60