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	$241.37	13.457%	$273.8512	$273.85	$273.85	$273.90
Purchase #2	$161.79	6.661%	$172.5668	$172.57	$172.55	$172.60
Purchase #3	$28.92	13.832%	$32.9202	$32.92	$32.90	$32.90
Purchase #4	$70.36	11.637%	$78.5478	$78.55	$78.55	$78.50
Purchase #5	$26.31	6.803%	$28.0999	$28.10	$28.10	$28.10
Purchase #6	$71.34	9.251%	$77.9397	$77.94	$77.95	$77.90
Purchase #7	$172.91	3.691%	$179.2921	$179.29	$179.30	$179.30
7 purchase totals =	$773.00		$843.2177	$843.22	$843.20	$843.20