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	$139.52	6.717%	$148.8916	$148.89	$148.90	$148.90
Purchase #2	$77.85	13.766%	$88.5668	$88.57	$88.55	$88.60
Purchase #3	$71.70	3.821%	$74.4397	$74.44	$74.45	$74.40
Purchase #4	$57.36	4.327%	$59.842	$59.84	$59.85	$59.80
Purchase #5	$140.36	3.490%	$145.2586	$145.26	$145.25	$145.30
Purchase #6	$108.50	10.435%	$119.822	$119.82	$119.80	$119.80
Purchase #7	$249.63	12.277%	$280.2771	$280.28	$280.30	$280.30
7 purchase totals =	$844.92		$917.0978	$917.10	$917.10	$917.10