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	$100.61	9.107%	$109.7726	$109.77	$109.75	$109.80
Purchase #2	$113.70	8.629%	$123.5112	$123.51	$123.50	$123.50
Purchase #3	$237.43	8.162%	$256.809	$256.81	$256.80	$256.80
Purchase #4	$38.26	4.278%	$39.8968	$39.90	$39.90	$39.90
Purchase #5	$139.32	4.429%	$145.4905	$145.49	$145.50	$145.50
Purchase #6	$54.49	7.188%	$58.4067	$58.41	$58.40	$58.40
Purchase #7	$115.53	4.678%	$120.9345	$120.93	$120.95	$120.90
7 purchase totals =	$799.34		$854.8213	$854.82	$854.80	$854.80