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	$8.28	12.636%	$9.3263	$9.33	$9.35	$9.30
Purchase #2	$121.31	13.310%	$137.4564	$137.46	$137.45	$137.50
Purchase #3	$196.66	10.570%	$217.447	$217.45	$217.45	$217.40
Purchase #4	$218.59	10.210%	$240.908	$240.91	$240.90	$240.90
Purchase #5	$146.71	7.343%	$157.4829	$157.48	$157.50	$157.50
Purchase #6	$133.84	6.421%	$142.4339	$142.43	$142.45	$142.40
Purchase #7	$167.76	10.565%	$185.4838	$185.48	$185.50	$185.50
7 purchase totals =	$993.15		$1,090.5383	$1,090.54	$1,090.60	$1,090.50