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	$141.40	6.791%	$151.0025	$151.00	$151.00	$151.00
Purchase #2	$244.97	9.747%	$268.8472	$268.85	$268.85	$268.80
Purchase #3	$90.91	11.558%	$101.4174	$101.42	$101.40	$101.40
Purchase #4	$137.94	13.714%	$156.8571	$156.86	$156.85	$156.90
Purchase #5	$132.81	10.874%	$147.2518	$147.25	$147.25	$147.30
Purchase #6	$111.59	13.114%	$126.2239	$126.22	$126.20	$126.20
Purchase #7	$6.86	9.701%	$7.5255	$7.53	$7.55	$7.50
7 purchase totals =	$866.48		$959.1254	$959.13	$959.10	$959.10