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	$29.50	11.825%	$32.9884	$32.99	$33.00	$33.00
Purchase #2	$215.89	8.322%	$233.8564	$233.86	$233.85	$233.90
Purchase #3	$82.44	5.808%	$87.2281	$87.23	$87.25	$87.20
Purchase #4	$32.56	11.535%	$36.3158	$36.32	$36.30	$36.30
Purchase #5	$38.79	9.605%	$42.5158	$42.52	$42.50	$42.50
Purchase #6	$54.76	12.127%	$61.4007	$61.40	$61.40	$61.40
Purchase #7	$175.37	4.606%	$183.4475	$183.45	$183.45	$183.40
7 purchase totals =	$629.31		$677.7527	$677.77	$677.75	$677.70