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	$24.84	12.430%	$27.9276	$27.93	$27.95	$27.90
Purchase #2	$41.77	11.326%	$46.5009	$46.50	$46.50	$46.50
Purchase #3	$122.80	11.439%	$136.8471	$136.85	$136.85	$136.80
Purchase #4	$55.51	13.213%	$62.8445	$62.84	$62.85	$62.80
Purchase #5	$106.78	5.589%	$112.7479	$112.75	$112.75	$112.70
Purchase #6	$171.82	10.389%	$189.6704	$189.67	$189.65	$189.70
Purchase #7	$86.43	4.520%	$90.3366	$90.34	$90.35	$90.30
7 purchase totals =	$609.95		$666.8750	$666.88	$666.90	$666.70