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	$137.49	6.828%	$146.8778	$146.88	$146.90	$146.90
Purchase #2	$81.63	12.452%	$91.7946	$91.79	$91.80	$91.80
Purchase #3	$20.53	12.784%	$23.1546	$23.15	$23.15	$23.20
Purchase #4	$202.43	6.351%	$215.2863	$215.29	$215.30	$215.30
Purchase #5	$93.46	7.267%	$100.2517	$100.25	$100.25	$100.30
Purchase #6	$92.61	10.653%	$102.4757	$102.48	$102.50	$102.50
Purchase #7	$240.30	10.597%	$265.7646	$265.76	$265.75	$265.80
7 purchase totals =	$868.45		$945.6053	$945.60	$945.65	$945.80