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	$76.55	11.759%	$85.5515	$85.55	$85.55	$85.60
Purchase #2	$23.73	13.307%	$26.8878	$26.89	$26.90	$26.90
Purchase #3	$109.29	12.547%	$123.0026	$123.00	$123.00	$123.00
Purchase #4	$26.42	9.568%	$28.9479	$28.95	$28.95	$28.90
Purchase #5	$139.86	3.290%	$144.4614	$144.46	$144.45	$144.50
Purchase #6	$12.96	12.405%	$14.5677	$14.57	$14.55	$14.60
Purchase #7	$107.47	8.796%	$116.9231	$116.92	$116.90	$116.90
7 purchase totals =	$496.28		$540.3420	$540.34	$540.30	$540.40