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	$75.53	6.731%	$80.6139	$80.61	$80.60	$80.60
Purchase #2	$70.55	7.494%	$75.837	$75.84	$75.85	$75.80
Purchase #3	$127.82	10.506%	$141.2488	$141.25	$141.25	$141.20
Purchase #4	$145.67	3.248%	$150.4014	$150.40	$150.40	$150.40
Purchase #5	$197.52	11.642%	$220.5153	$220.52	$220.50	$220.50
Purchase #6	$90.81	9.688%	$99.6077	$99.61	$99.60	$99.60
Purchase #7	$207.39	13.303%	$234.9791	$234.98	$235.00	$235.00
7 purchase totals =	$915.29		$1,003.2032	$1,003.21	$1,003.20	$1,003.10