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	$133.42	4.360%	$139.2371	$139.24	$139.25	$139.20
Purchase #2	$85.66	12.679%	$96.5208	$96.52	$96.50	$96.50
Purchase #3	$244.33	10.733%	$270.5539	$270.55	$270.55	$270.60
Purchase #4	$70.78	6.735%	$75.547	$75.55	$75.55	$75.50
Purchase #5	$205.83	6.227%	$218.647	$218.65	$218.65	$218.60
Purchase #6	$126.83	13.545%	$144.0091	$144.01	$144.00	$144.00
Purchase #7	$213.59	9.442%	$233.7572	$233.76	$233.75	$233.80
7 purchase totals =	$1,080.44		$1,178.2721	$1,178.28	$1,178.25	$1,178.20