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	$99.82	6.463%	$106.2714	$106.27	$106.25	$106.30
Purchase #2	$171.50	6.845%	$183.2392	$183.24	$183.25	$183.20
Purchase #3	$194.76	12.561%	$219.2238	$219.22	$219.20	$219.20
Purchase #4	$106.38	7.683%	$114.5532	$114.55	$114.55	$114.60
Purchase #5	$112.88	5.806%	$119.4338	$119.43	$119.45	$119.40
Purchase #6	$249.25	10.454%	$275.3066	$275.31	$275.30	$275.30
Purchase #7	$170.92	6.649%	$182.2845	$182.28	$182.30	$182.30
7 purchase totals =	$1,105.51		$1,200.3125	$1,200.30	$1,200.30	$1,200.30