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	$42.45	7.176%	$45.4962	$45.50	$45.50	$45.50
Purchase #2	$60.50	11.759%	$67.6142	$67.61	$67.60	$67.60
Purchase #3	$150.85	9.580%	$165.3014	$165.30	$165.30	$165.30
Purchase #4	$144.59	13.633%	$164.302	$164.30	$164.30	$164.30
Purchase #5	$81.75	5.799%	$86.4907	$86.49	$86.50	$86.50
Purchase #6	$226.86	7.143%	$243.0646	$243.06	$243.05	$243.10
Purchase #7	$33.55	13.357%	$38.0313	$38.03	$38.05	$38.00
7 purchase totals =	$740.55		$810.3004	$810.29	$810.30	$810.30