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	$51.76	11.198%	$57.5561	$57.56	$57.55	$57.60
Purchase #2	$82.28	9.198%	$89.8481	$89.85	$89.85	$89.80
Purchase #3	$207.32	12.473%	$233.179	$233.18	$233.20	$233.20
Purchase #4	$111.30	5.250%	$117.1433	$117.14	$117.15	$117.10
Purchase #5	$109.39	3.853%	$113.6048	$113.60	$113.60	$113.60
Purchase #6	$86.88	6.653%	$92.6601	$92.66	$92.65	$92.70
Purchase #7	$172.42	4.869%	$180.8151	$180.82	$180.80	$180.80
7 purchase totals =	$821.35		$884.8065	$884.81	$884.80	$884.80