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	$239.68	8.686%	$260.4986	$260.50	$260.50	$260.50
Purchase #2	$91.69	9.662%	$100.5491	$100.55	$100.55	$100.50
Purchase #3	$232.28	11.620%	$259.2709	$259.27	$259.25	$259.30
Purchase #4	$161.30	13.481%	$183.0449	$183.04	$183.05	$183.00
Purchase #5	$78.64	6.225%	$83.5353	$83.54	$83.55	$83.50
Purchase #6	$130.44	7.118%	$139.7247	$139.72	$139.70	$139.70
Purchase #7	$55.95	6.637%	$59.6634	$59.66	$59.65	$59.70
7 purchase totals =	$989.98		$1,086.2869	$1,086.28	$1,086.25	$1,086.20