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	$24.78	8.521%	$26.8915	$26.89	$26.90	$26.90
Purchase #2	$121.92	4.865%	$127.8514	$127.85	$127.85	$127.90
Purchase #3	$55.57	3.168%	$57.3305	$57.33	$57.35	$57.30
Purchase #4	$82.85	7.872%	$89.372	$89.37	$89.35	$89.40
Purchase #5	$217.47	13.489%	$246.8045	$246.80	$246.80	$246.80
Purchase #6	$171.49	5.296%	$180.5721	$180.57	$180.55	$180.60
Purchase #7	$113.55	6.173%	$120.5594	$120.56	$120.55	$120.60
7 purchase totals =	$787.63		$849.3814	$849.37	$849.35	$849.50