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	$52.93	12.294%	$59.4372	$59.44	$59.45	$59.40
Purchase #2	$51.86	4.632%	$54.2622	$54.26	$54.25	$54.30
Purchase #3	$206.46	12.517%	$232.3026	$232.30	$232.30	$232.30
Purchase #4	$40.38	3.116%	$41.6382	$41.64	$41.65	$41.60
Purchase #5	$18.69	8.865%	$20.3469	$20.35	$20.35	$20.30
Purchase #6	$236.26	5.773%	$249.8993	$249.90	$249.90	$249.90
Purchase #7	$57.26	9.123%	$62.4838	$62.48	$62.50	$62.50
7 purchase totals =	$663.84		$720.3702	$720.37	$720.40	$720.30