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	$56.78	11.275%	$63.1819	$63.18	$63.20	$63.20
Purchase #2	$163.57	8.714%	$177.8235	$177.82	$177.80	$177.80
Purchase #3	$167.51	10.128%	$184.4754	$184.48	$184.50	$184.50
Purchase #4	$71.32	3.606%	$73.8918	$73.89	$73.90	$73.90
Purchase #5	$95.35	4.297%	$99.4472	$99.45	$99.45	$99.40
Purchase #6	$89.54	10.321%	$98.7814	$98.78	$98.80	$98.80
Purchase #7	$149.47	12.616%	$168.3271	$168.33	$168.35	$168.30
7 purchase totals =	$793.54		$865.9283	$865.93	$866.00	$865.90