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	$49.66	6.727%	$53.0006	$53.00	$53.00	$53.00
Purchase #2	$202.35	13.611%	$229.8919	$229.89	$229.90	$229.90
Purchase #3	$113.97	8.246%	$123.368	$123.37	$123.35	$123.40
Purchase #4	$121.34	5.355%	$127.8378	$127.84	$127.85	$127.80
Purchase #5	$37.49	6.752%	$40.0213	$40.02	$40.00	$40.00
Purchase #6	$105.73	10.568%	$116.9035	$116.90	$116.90	$116.90
Purchase #7	$30.59	5.508%	$32.2749	$32.27	$32.25	$32.30
7 purchase totals =	$661.13		$723.2980	$723.29	$723.25	$723.30