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	$216.56	11.201%	$240.8169	$240.82	$240.80	$240.80
Purchase #2	$83.67	7.534%	$89.9737	$89.97	$89.95	$90.00
Purchase #3	$186.76	5.140%	$196.3595	$196.36	$196.35	$196.40
Purchase #4	$93.84	12.276%	$105.3598	$105.36	$105.35	$105.40
Purchase #5	$107.48	12.732%	$121.1644	$121.16	$121.15	$121.20
Purchase #6	$133.71	8.586%	$145.1903	$145.19	$145.20	$145.20
Purchase #7	$91.36	9.833%	$100.3434	$100.34	$100.35	$100.30
7 purchase totals =	$913.38		$999.2080	$999.20	$999.15	$999.30