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	$117.41	12.242%	$131.7833	$131.78	$131.80	$131.80
Purchase #2	$247.49	9.359%	$270.6526	$270.65	$270.65	$270.70
Purchase #3	$41.48	8.794%	$45.1278	$45.13	$45.15	$45.10
Purchase #4	$100.56	11.864%	$112.4904	$112.49	$112.50	$112.50
Purchase #5	$47.30	10.643%	$52.3341	$52.33	$52.35	$52.30
Purchase #6	$242.31	13.183%	$274.2537	$274.25	$274.25	$274.30
Purchase #7	$96.86	6.858%	$103.5027	$103.50	$103.50	$103.50
7 purchase totals =	$893.41		$990.1446	$990.13	$990.20	$990.20