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	$54.56	9.791%	$59.902	$59.90	$59.90	$59.90
Purchase #2	$43.62	6.402%	$46.4126	$46.41	$46.40	$46.40
Purchase #3	$209.32	6.396%	$222.7081	$222.71	$222.70	$222.70
Purchase #4	$188.70	5.427%	$198.9407	$198.94	$198.95	$198.90
Purchase #5	$95.88	4.120%	$99.8303	$99.83	$99.85	$99.80
Purchase #6	$227.65	11.657%	$254.1872	$254.19	$254.20	$254.20
Purchase #7	$114.76	12.822%	$129.4745	$129.47	$129.45	$129.50
7 purchase totals =	$934.49		$1,011.4554	$1,011.45	$1,011.45	$1,011.40