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	$133.57	6.714%	$142.5379	$142.54	$142.55	$142.50
Purchase #2	$86.49	9.573%	$94.7697	$94.77	$94.75	$94.80
Purchase #3	$184.99	13.696%	$210.3262	$210.33	$210.35	$210.30
Purchase #4	$44.44	13.561%	$50.4665	$50.47	$50.45	$50.50
Purchase #5	$153.86	8.574%	$167.052	$167.05	$167.05	$167.10
Purchase #6	$74.51	3.798%	$77.3399	$77.34	$77.35	$77.30
Purchase #7	$85.73	6.123%	$90.9792	$90.98	$91.00	$91.00
7 purchase totals =	$763.59		$833.4714	$833.48	$833.50	$833.50