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	$239.35	13.576%	$271.8442	$271.84	$271.85	$271.80
Purchase #2	$179.76	6.868%	$192.1059	$192.11	$192.10	$192.10
Purchase #3	$90.64	7.381%	$97.3301	$97.33	$97.35	$97.30
Purchase #4	$113.61	5.471%	$119.8256	$119.83	$119.85	$119.80
Purchase #5	$127.32	3.299%	$131.5203	$131.52	$131.50	$131.50
Purchase #6	$100.90	3.401%	$104.3316	$104.33	$104.35	$104.30
Purchase #7	$45.46	10.814%	$50.376	$50.38	$50.40	$50.40
7 purchase totals =	$897.04		$967.3337	$967.34	$967.40	$967.20