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	$71.68	3.769%	$74.3816	$74.38	$74.40	$74.40
Purchase #2	$122.46	11.845%	$136.9654	$136.97	$136.95	$137.00
Purchase #3	$82.65	8.689%	$89.8315	$89.83	$89.85	$89.80
Purchase #4	$206.37	7.514%	$221.8766	$221.88	$221.90	$221.90
Purchase #5	$206.34	6.295%	$219.3291	$219.33	$219.35	$219.30
Purchase #6	$217.43	12.186%	$243.926	$243.93	$243.95	$243.90
Purchase #7	$86.59	3.374%	$89.5115	$89.51	$89.50	$89.50
7 purchase totals =	$993.52		$1,075.8217	$1,075.83	$1,075.90	$1,075.80