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	$82.42	10.668%	$91.2126	$91.21	$91.20	$91.20
Purchase #2	$206.50	6.526%	$219.9762	$219.98	$220.00	$220.00
Purchase #3	$118.47	4.170%	$123.4102	$123.41	$123.40	$123.40
Purchase #4	$102.67	10.586%	$113.5386	$113.54	$113.55	$113.50
Purchase #5	$86.79	4.647%	$90.8231	$90.82	$90.80	$90.80
Purchase #6	$199.75	8.251%	$216.2314	$216.23	$216.25	$216.20
Purchase #7	$71.68	12.150%	$80.3891	$80.39	$80.40	$80.40
7 purchase totals =	$868.28		$935.5812	$935.58	$935.60	$935.50