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	$67.64	9.288%	$73.9224	$73.92	$73.90	$73.90
Purchase #2	$164.75	12.794%	$185.8281	$185.83	$185.85	$185.80
Purchase #3	$87.30	3.131%	$90.0334	$90.03	$90.05	$90.00
Purchase #4	$242.42	13.252%	$274.5455	$274.55	$274.55	$274.50
Purchase #5	$188.80	4.294%	$196.9071	$196.91	$196.90	$196.90
Purchase #6	$141.90	5.549%	$149.774	$149.77	$149.75	$149.80
Purchase #7	$249.37	4.265%	$260.0056	$260.01	$260.00	$260.00
7 purchase totals =	$1,142.18		$1,231.0161	$1,231.02	$1,231.00	$1,230.90