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	$87.58	3.247%	$90.4237	$90.42	$90.40	$90.40
Purchase #2	$73.33	13.104%	$82.9392	$82.94	$82.95	$82.90
Purchase #3	$55.28	8.161%	$59.7914	$59.79	$59.80	$59.80
Purchase #4	$248.72	4.155%	$259.0543	$259.05	$259.05	$259.10
Purchase #5	$160.94	4.453%	$168.1067	$168.11	$168.10	$168.10
Purchase #6	$25.36	7.809%	$27.3404	$27.34	$27.35	$27.30
Purchase #7	$90.29	13.745%	$102.7004	$102.70	$102.70	$102.70
7 purchase totals =	$741.50		$790.3561	$790.35	$790.35	$790.30