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	$250.32	3.580%	$259.2815	$259.28	$259.30	$259.30
Purchase #2	$183.99	5.124%	$193.4176	$193.42	$193.40	$193.40
Purchase #3	$203.49	12.725%	$229.3841	$229.38	$229.40	$229.40
Purchase #4	$39.31	6.524%	$41.8746	$41.87	$41.85	$41.90
Purchase #5	$95.29	6.277%	$101.2714	$101.27	$101.25	$101.30
Purchase #6	$94.57	6.182%	$100.4163	$100.42	$100.40	$100.40
Purchase #7	$212.36	5.754%	$224.5792	$224.58	$224.60	$224.60
7 purchase totals =	$1,079.33		$1,150.2247	$1,150.22	$1,150.20	$1,150.30