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	$45.73	9.494%	$50.0716	$50.07	$50.05	$50.10
Purchase #2	$87.36	4.214%	$91.0414	$91.04	$91.05	$91.00
Purchase #3	$67.30	7.688%	$72.474	$72.47	$72.45	$72.50
Purchase #4	$29.42	7.112%	$31.5124	$31.51	$31.50	$31.50
Purchase #5	$138.67	4.247%	$144.5593	$144.56	$144.55	$144.60
Purchase #6	$62.60	11.544%	$69.8265	$69.83	$69.85	$69.80
Purchase #7	$210.36	7.155%	$225.4113	$225.41	$225.40	$225.40
7 purchase totals =	$641.44		$684.8965	$684.89	$684.85	$684.90