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	$39.81	8.293%	$43.1114	$43.11	$43.10	$43.10
Purchase #2	$94.61	8.756%	$102.8941	$102.89	$102.90	$102.90
Purchase #3	$54.89	8.693%	$59.6616	$59.66	$59.65	$59.70
Purchase #4	$47.71	8.810%	$51.9133	$51.91	$51.90	$51.90
Purchase #5	$183.55	9.239%	$200.5082	$200.51	$200.50	$200.50
Purchase #6	$123.32	13.427%	$139.8782	$139.88	$139.90	$139.90
Purchase #7	$88.50	7.563%	$95.1933	$95.19	$95.20	$95.20
7 purchase totals =	$632.39		$693.1601	$693.15	$693.15	$693.20