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	$243.46	12.759%	$274.5231	$274.52	$274.50	$274.50
Purchase #2	$99.62	4.153%	$103.7572	$103.76	$103.75	$103.80
Purchase #3	$157.90	3.167%	$162.9007	$162.90	$162.90	$162.90
Purchase #4	$10.57	13.245%	$11.97	$11.97	$11.95	$12.00
Purchase #5	$147.82	5.440%	$155.8614	$155.86	$155.85	$155.90
Purchase #6	$249.45	11.488%	$278.1068	$278.11	$278.10	$278.10
Purchase #7	$92.25	12.163%	$103.4704	$103.47	$103.45	$103.50
7 purchase totals =	$1,001.07		$1,090.5896	$1,090.59	$1,090.50	$1,090.70