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	$17.71	13.560%	$20.1115	$20.11	$20.10	$20.10
Purchase #2	$79.52	4.338%	$82.9696	$82.97	$82.95	$83.00
Purchase #3	$139.66	13.523%	$158.5462	$158.55	$158.55	$158.50
Purchase #4	$11.91	13.164%	$13.4778	$13.48	$13.50	$13.50
Purchase #5	$32.37	3.296%	$33.4369	$33.44	$33.45	$33.40
Purchase #6	$7.69	10.558%	$8.5019	$8.50	$8.50	$8.50
Purchase #7	$144.99	3.728%	$150.3952	$150.40	$150.40	$150.40
7 purchase totals =	$433.85		$467.4391	$467.45	$467.45	$467.40