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	$52.98	4.416%	$55.3196	$55.32	$55.30	$55.30
Purchase #2	$69.53	4.709%	$72.8042	$72.80	$72.80	$72.80
Purchase #3	$238.93	13.147%	$270.3421	$270.34	$270.35	$270.30
Purchase #4	$41.93	7.442%	$45.0504	$45.05	$45.05	$45.10
Purchase #5	$153.62	12.619%	$173.0053	$173.01	$173.00	$173.00
Purchase #6	$57.55	5.737%	$60.8516	$60.85	$60.85	$60.90
Purchase #7	$84.76	6.827%	$90.5466	$90.55	$90.55	$90.50
7 purchase totals =	$699.30		$767.9198	$767.92	$767.90	$767.90