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	$41.51	9.134%	$45.3015	$45.30	$45.30	$45.30
Purchase #2	$72.83	12.456%	$81.9017	$81.90	$81.90	$81.90
Purchase #3	$33.79	13.704%	$38.4206	$38.42	$38.40	$38.40
Purchase #4	$23.45	8.674%	$25.4841	$25.48	$25.50	$25.50
Purchase #5	$236.97	7.291%	$254.2475	$254.25	$254.25	$254.20
Purchase #6	$164.71	12.483%	$185.2707	$185.27	$185.25	$185.30
Purchase #7	$134.34	5.218%	$141.3499	$141.35	$141.35	$141.30
7 purchase totals =	$707.60		$771.9760	$771.97	$771.95	$771.90