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	$244.87	12.318%	$275.0331	$275.03	$275.05	$275.00
Purchase #2	$84.77	12.666%	$95.507	$95.51	$95.50	$95.50
Purchase #3	$164.30	13.709%	$186.8239	$186.82	$186.80	$186.80
Purchase #4	$84.35	8.450%	$91.4776	$91.48	$91.50	$91.50
Purchase #5	$59.83	5.857%	$63.3342	$63.33	$63.35	$63.30
Purchase #6	$111.42	6.498%	$118.6601	$118.66	$118.65	$118.70
Purchase #7	$233.25	4.294%	$243.2658	$243.27	$243.25	$243.30
7 purchase totals =	$982.79		$1,074.1017	$1,074.10	$1,074.10	$1,074.10