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	$95.70	5.243%	$100.7176	$100.72	$100.70	$100.70
Purchase #2	$131.48	9.190%	$143.563	$143.56	$143.55	$143.60
Purchase #3	$95.78	7.427%	$102.8936	$102.89	$102.90	$102.90
Purchase #4	$89.42	7.251%	$95.9038	$95.90	$95.90	$95.90
Purchase #5	$130.39	11.685%	$145.6261	$145.63	$145.65	$145.60
Purchase #6	$46.88	11.358%	$52.2046	$52.20	$52.20	$52.20
Purchase #7	$142.44	4.563%	$148.9395	$148.94	$148.95	$148.90
7 purchase totals =	$732.09		$789.8482	$789.84	$789.85	$789.80