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	$31.50	7.777%	$33.9498	$33.95	$33.95	$33.90
Purchase #2	$33.30	13.566%	$37.8175	$37.82	$37.80	$37.80
Purchase #3	$52.83	5.107%	$55.528	$55.53	$55.55	$55.50
Purchase #4	$128.60	10.356%	$141.9178	$141.92	$141.90	$141.90
Purchase #5	$61.32	6.341%	$65.2083	$65.21	$65.20	$65.20
Purchase #6	$11.88	12.212%	$13.3308	$13.33	$13.35	$13.30
Purchase #7	$145.71	5.281%	$153.4049	$153.40	$153.40	$153.40
7 purchase totals =	$465.14		$501.1571	$501.16	$501.15	$501.00