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	$93.58	10.640%	$103.5369	$103.54	$103.55	$103.50
Purchase #2	$25.41	8.693%	$27.6189	$27.62	$27.60	$27.60
Purchase #3	$84.49	12.346%	$94.9211	$94.92	$94.90	$94.90
Purchase #4	$13.45	7.591%	$14.471	$14.47	$14.45	$14.50
Purchase #5	$82.77	3.766%	$85.8871	$85.89	$85.90	$85.90
Purchase #6	$242.40	13.190%	$274.3726	$274.37	$274.35	$274.40
Purchase #7	$211.97	3.559%	$219.514	$219.51	$219.50	$219.50
7 purchase totals =	$754.07		$820.3216	$820.32	$820.25	$820.30