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	$83.75	6.380%	$89.0933	$89.09	$89.10	$89.10
Purchase #2	$174.55	12.541%	$196.4403	$196.44	$196.45	$196.40
Purchase #3	$161.98	11.823%	$181.1309	$181.13	$181.15	$181.10
Purchase #4	$62.74	13.585%	$71.2632	$71.26	$71.25	$71.30
Purchase #5	$32.72	11.241%	$36.3981	$36.40	$36.40	$36.40
Purchase #6	$122.45	12.365%	$137.5909	$137.59	$137.60	$137.60
Purchase #7	$180.31	5.570%	$190.3533	$190.35	$190.35	$190.40
7 purchase totals =	$818.50		$902.2700	$902.26	$902.30	$902.30