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	$83.67	7.381%	$89.8457	$89.85	$89.85	$89.80
Purchase #2	$76.69	7.545%	$82.4763	$82.48	$82.50	$82.50
Purchase #3	$57.33	3.840%	$59.5315	$59.53	$59.55	$59.50
Purchase #4	$207.86	8.489%	$225.5052	$225.51	$225.50	$225.50
Purchase #5	$218.91	13.831%	$249.1874	$249.19	$249.20	$249.20
Purchase #6	$153.92	9.854%	$169.0873	$169.09	$169.10	$169.10
Purchase #7	$20.50	10.281%	$22.6076	$22.61	$22.60	$22.60
7 purchase totals =	$818.88		$898.2410	$898.26	$898.30	$898.20