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	$90.52	3.767%	$93.9299	$93.93	$93.95	$93.90
Purchase #2	$210.43	6.366%	$223.826	$223.83	$223.85	$223.80
Purchase #3	$54.50	8.561%	$59.1657	$59.17	$59.15	$59.20
Purchase #4	$40.85	6.351%	$43.4444	$43.44	$43.45	$43.40
Purchase #5	$196.78	5.841%	$208.2739	$208.27	$208.25	$208.30
Purchase #6	$241.40	4.365%	$251.9371	$251.94	$251.95	$251.90
Purchase #7	$39.27	8.646%	$42.6653	$42.67	$42.65	$42.70
7 purchase totals =	$873.75		$923.2423	$923.25	$923.25	$923.20