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	$167.47	10.651%	$185.3072	$185.31	$185.30	$185.30
Purchase #2	$88.59	8.801%	$96.3868	$96.39	$96.40	$96.40
Purchase #3	$182.29	8.860%	$198.4409	$198.44	$198.45	$198.40
Purchase #4	$48.57	3.599%	$50.318	$50.32	$50.30	$50.30
Purchase #5	$94.55	9.631%	$103.6561	$103.66	$103.65	$103.70
Purchase #6	$15.51	7.164%	$16.6211	$16.62	$16.60	$16.60
Purchase #7	$13.29	11.319%	$14.7943	$14.79	$14.80	$14.80
7 purchase totals =	$610.27		$665.5244	$665.53	$665.50	$665.50