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	$169.32	9.368%	$185.1819	$185.18	$185.20	$185.20
Purchase #2	$73.81	13.557%	$83.8164	$83.82	$83.80	$83.80
Purchase #3	$207.51	6.606%	$221.2181	$221.22	$221.20	$221.20
Purchase #4	$87.86	10.305%	$96.914	$96.91	$96.90	$96.90
Purchase #5	$166.51	3.514%	$172.3612	$172.36	$172.35	$172.40
Purchase #6	$37.67	4.116%	$39.2205	$39.22	$39.20	$39.20
Purchase #7	$133.63	10.239%	$147.3124	$147.31	$147.30	$147.30
7 purchase totals =	$876.31		$946.0245	$946.02	$945.95	$946.00