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	$180.35	5.120%	$189.5839	$189.58	$189.60	$189.60
Purchase #2	$51.61	4.679%	$54.0248	$54.02	$54.00	$54.00
Purchase #3	$167.86	5.576%	$177.2199	$177.22	$177.20	$177.20
Purchase #4	$82.35	5.562%	$86.9303	$86.93	$86.95	$86.90
Purchase #5	$82.46	9.161%	$90.0142	$90.01	$90.00	$90.00
Purchase #6	$67.83	6.236%	$72.0599	$72.06	$72.05	$72.10
Purchase #7	$69.98	4.409%	$73.0654	$73.07	$73.05	$73.10
7 purchase totals =	$702.44		$742.8984	$742.89	$742.85	$742.90