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	$53.25	12.270%	$59.7838	$59.78	$59.80	$59.80
Purchase #2	$88.34	13.641%	$100.3905	$100.39	$100.40	$100.40
Purchase #3	$187.44	13.110%	$212.0134	$212.01	$212.00	$212.00
Purchase #4	$143.52	9.460%	$157.097	$157.10	$157.10	$157.10
Purchase #5	$47.49	6.588%	$50.6186	$50.62	$50.60	$50.60
Purchase #6	$64.47	9.301%	$70.4664	$70.47	$70.45	$70.50
Purchase #7	$139.33	13.402%	$158.003	$158.00	$158.00	$158.00
7 purchase totals =	$723.84		$808.3727	$808.37	$808.35	$808.40