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	$152.29	7.812%	$164.1869	$164.19	$164.20	$164.20
Purchase #2	$205.78	6.221%	$218.5816	$218.58	$218.60	$218.60
Purchase #3	$111.37	13.258%	$126.1354	$126.14	$126.15	$126.10
Purchase #4	$147.81	11.618%	$164.9826	$164.98	$165.00	$165.00
Purchase #5	$76.88	11.104%	$85.4168	$85.42	$85.40	$85.40
Purchase #6	$64.53	6.682%	$68.8419	$68.84	$68.85	$68.80
Purchase #7	$140.89	7.250%	$151.1045	$151.10	$151.10	$151.10
7 purchase totals =	$899.55		$979.2497	$979.25	$979.30	$979.20