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	$34.56	3.111%	$35.6352	$35.64	$35.65	$35.60
Purchase #2	$91.78	4.387%	$95.8064	$95.81	$95.80	$95.80
Purchase #3	$131.65	12.780%	$148.4749	$148.47	$148.45	$148.50
Purchase #4	$204.87	8.485%	$222.2532	$222.25	$222.25	$222.30
Purchase #5	$167.84	7.558%	$180.5253	$180.53	$180.55	$180.50
Purchase #6	$97.30	3.120%	$100.3358	$100.34	$100.35	$100.30
Purchase #7	$68.77	8.841%	$74.85	$74.85	$74.85	$74.90
7 purchase totals =	$796.77		$857.8808	$857.89	$857.90	$857.90