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	$92.36	8.411%	$100.1284	$100.13	$100.15	$100.10
Purchase #2	$37.78	7.169%	$40.4884	$40.49	$40.50	$40.50
Purchase #3	$51.35	10.706%	$56.8475	$56.85	$56.85	$56.80
Purchase #4	$234.88	12.635%	$264.5571	$264.56	$264.55	$264.60
Purchase #5	$119.95	11.532%	$133.7826	$133.78	$133.80	$133.80
Purchase #6	$238.51	3.230%	$246.2139	$246.21	$246.20	$246.20
Purchase #7	$179.50	3.798%	$186.3174	$186.32	$186.30	$186.30
7 purchase totals =	$954.33		$1,028.3353	$1,028.34	$1,028.35	$1,028.30