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	$98.78	12.458%	$111.086	$111.09	$111.10	$111.10
Purchase #2	$142.40	5.706%	$150.5253	$150.53	$150.55	$150.50
Purchase #3	$177.35	4.252%	$184.8909	$184.89	$184.90	$184.90
Purchase #4	$125.74	7.793%	$135.5389	$135.54	$135.55	$135.50
Purchase #5	$184.86	8.232%	$200.0777	$200.08	$200.10	$200.10
Purchase #6	$41.51	11.786%	$46.4024	$46.40	$46.40	$46.40
Purchase #7	$75.56	3.105%	$77.9061	$77.91	$77.90	$77.90
7 purchase totals =	$846.20		$906.4273	$906.44	$906.50	$906.40