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	$18.35	10.107%	$20.2046	$20.20	$20.20	$20.20
Purchase #2	$37.74	10.699%	$41.7778	$41.78	$41.80	$41.80
Purchase #3	$217.49	5.803%	$230.1109	$230.11	$230.10	$230.10
Purchase #4	$207.70	7.218%	$222.6918	$222.69	$222.70	$222.70
Purchase #5	$29.89	13.225%	$33.843	$33.84	$33.85	$33.80
Purchase #6	$220.40	8.119%	$238.2943	$238.29	$238.30	$238.30
Purchase #7	$85.41	7.189%	$91.5501	$91.55	$91.55	$91.60
7 purchase totals =	$816.98		$878.4725	$878.46	$878.50	$878.50