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	$83.99	6.341%	$89.3158	$89.32	$89.30	$89.30
Purchase #2	$240.37	3.632%	$249.1002	$249.10	$249.10	$249.10
Purchase #3	$232.77	4.555%	$243.3727	$243.37	$243.35	$243.40
Purchase #4	$31.85	5.723%	$33.6728	$33.67	$33.65	$33.70
Purchase #5	$37.73	12.733%	$42.5342	$42.53	$42.55	$42.50
Purchase #6	$38.88	5.832%	$41.1475	$41.15	$41.15	$41.10
Purchase #7	$61.96	8.145%	$67.0066	$67.01	$67.00	$67.00
7 purchase totals =	$727.55		$766.1498	$766.15	$766.10	$766.10