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	$237.43	11.539%	$264.827	$264.83	$264.85	$264.80
Purchase #2	$117.40	7.766%	$126.5173	$126.52	$126.50	$126.50
Purchase #3	$36.55	6.231%	$38.8274	$38.83	$38.85	$38.80
Purchase #4	$164.66	12.446%	$185.1536	$185.15	$185.15	$185.20
Purchase #5	$133.92	4.855%	$140.4218	$140.42	$140.40	$140.40
Purchase #6	$37.71	9.185%	$41.1737	$41.17	$41.15	$41.20
Purchase #7	$104.71	12.550%	$117.8511	$117.85	$117.85	$117.90
7 purchase totals =	$832.38		$914.7719	$914.77	$914.75	$914.80