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	$31.68	13.874%	$36.0753	$36.08	$36.10	$36.10
Purchase #2	$95.58	3.592%	$99.0132	$99.01	$99.00	$99.00
Purchase #3	$150.40	13.828%	$171.1973	$171.20	$171.20	$171.20
Purchase #4	$148.73	10.317%	$164.0745	$164.07	$164.05	$164.10
Purchase #5	$39.41	10.213%	$43.4349	$43.43	$43.45	$43.40
Purchase #6	$86.67	12.487%	$97.4925	$97.49	$97.50	$97.50
Purchase #7	$207.94	3.689%	$215.6109	$215.61	$215.60	$215.60
7 purchase totals =	$760.41		$826.8986	$826.89	$826.90	$826.90