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	$39.84	8.362%	$43.1714	$43.17	$43.15	$43.20
Purchase #2	$114.81	11.477%	$127.9867	$127.99	$128.00	$128.00
Purchase #3	$118.66	11.118%	$131.8526	$131.85	$131.85	$131.90
Purchase #4	$101.35	3.267%	$104.6611	$104.66	$104.65	$104.70
Purchase #5	$95.46	3.359%	$98.6665	$98.67	$98.65	$98.70
Purchase #6	$240.92	13.844%	$274.273	$274.27	$274.25	$274.30
Purchase #7	$143.79	4.627%	$150.4432	$150.44	$150.45	$150.40
7 purchase totals =	$854.83		$931.0545	$931.05	$931.00	$931.20