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	$41.47	9.314%	$45.3325	$45.33	$45.35	$45.30
Purchase #2	$164.92	9.342%	$180.3268	$180.33	$180.35	$180.30
Purchase #3	$63.64	13.350%	$72.1359	$72.14	$72.15	$72.10
Purchase #4	$208.54	3.860%	$216.5896	$216.59	$216.60	$216.60
Purchase #5	$194.29	12.110%	$217.8185	$217.82	$217.80	$217.80
Purchase #6	$20.57	6.641%	$21.9361	$21.94	$21.95	$21.90
Purchase #7	$31.84	12.409%	$35.791	$35.79	$35.80	$35.80
7 purchase totals =	$725.27		$789.9304	$789.94	$790.00	$789.80