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	$31.98	5.709%	$33.8057	$33.81	$33.80	$33.80
Purchase #2	$20.75	7.213%	$22.2467	$22.25	$22.25	$22.20
Purchase #3	$232.61	9.771%	$255.3383	$255.34	$255.35	$255.30
Purchase #4	$85.75	12.587%	$96.5434	$96.54	$96.55	$96.50
Purchase #5	$121.65	13.356%	$137.8976	$137.90	$137.90	$137.90
Purchase #6	$98.73	7.205%	$105.8435	$105.84	$105.85	$105.80
Purchase #7	$13.45	5.736%	$14.2215	$14.22	$14.20	$14.20
7 purchase totals =	$604.92		$665.8967	$665.90	$665.90	$665.70