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	$55.32	13.743%	$62.9226	$62.92	$62.90	$62.90
Purchase #2	$31.38	6.463%	$33.4081	$33.41	$33.40	$33.40
Purchase #3	$214.33	10.264%	$236.3288	$236.33	$236.35	$236.30
Purchase #4	$99.27	9.693%	$108.8922	$108.89	$108.90	$108.90
Purchase #5	$196.94	10.290%	$217.2051	$217.21	$217.20	$217.20
Purchase #6	$32.86	13.870%	$37.4177	$37.42	$37.40	$37.40
Purchase #7	$131.52	5.459%	$138.6997	$138.70	$138.70	$138.70
7 purchase totals =	$761.62		$834.8742	$834.88	$834.85	$834.80