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	$250.30	12.841%	$282.441	$282.44	$282.45	$282.40
Purchase #2	$227.48	12.588%	$256.1152	$256.12	$256.10	$256.10
Purchase #3	$90.32	7.198%	$96.8212	$96.82	$96.80	$96.80
Purchase #4	$84.68	6.639%	$90.3019	$90.30	$90.30	$90.30
Purchase #5	$95.81	4.244%	$99.8762	$99.88	$99.90	$99.90
Purchase #6	$215.88	7.175%	$231.3694	$231.37	$231.35	$231.40
Purchase #7	$135.63	5.869%	$143.5901	$143.59	$143.60	$143.60
7 purchase totals =	$1,100.10		$1,200.5150	$1,200.52	$1,200.50	$1,200.50