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	$54.47	8.752%	$59.2372	$59.24	$59.25	$59.20
Purchase #2	$197.47	13.299%	$223.7315	$223.73	$223.75	$223.70
Purchase #3	$246.59	5.225%	$259.4743	$259.47	$259.45	$259.50
Purchase #4	$139.89	13.113%	$158.2338	$158.23	$158.25	$158.20
Purchase #5	$181.44	8.374%	$196.6338	$196.63	$196.65	$196.60
Purchase #6	$51.81	3.287%	$53.513	$53.51	$53.50	$53.50
Purchase #7	$20.94	9.594%	$22.949	$22.95	$22.95	$22.90
7 purchase totals =	$892.61		$973.7726	$973.76	$973.80	$973.60