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	$23.94	12.454%	$26.9215	$26.92	$26.90	$26.90
Purchase #2	$36.63	9.453%	$40.0926	$40.09	$40.10	$40.10
Purchase #3	$152.50	7.850%	$164.4713	$164.47	$164.45	$164.50
Purchase #4	$130.93	6.751%	$139.7691	$139.77	$139.75	$139.80
Purchase #5	$36.92	7.735%	$39.7758	$39.78	$39.80	$39.80
Purchase #6	$67.98	5.314%	$71.5925	$71.59	$71.60	$71.60
Purchase #7	$88.73	13.140%	$100.3891	$100.39	$100.40	$100.40
7 purchase totals =	$537.63		$583.0119	$583.01	$583.00	$583.10