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	$97.41	8.695%	$105.8798	$105.88	$105.90	$105.90
Purchase #2	$239.98	6.838%	$256.3898	$256.39	$256.40	$256.40
Purchase #3	$133.44	5.231%	$140.4202	$140.42	$140.40	$140.40
Purchase #4	$54.53	3.301%	$56.33	$56.33	$56.35	$56.30
Purchase #5	$18.50	10.390%	$20.4222	$20.42	$20.40	$20.40
Purchase #6	$93.96	7.873%	$101.3575	$101.36	$101.35	$101.40
Purchase #7	$222.33	5.540%	$234.6471	$234.65	$234.65	$234.60
7 purchase totals =	$860.15		$915.4466	$915.45	$915.45	$915.40