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	$71.59	10.205%	$78.8958	$78.90	$78.90	$78.90
Purchase #2	$225.46	9.291%	$246.4075	$246.41	$246.40	$246.40
Purchase #3	$46.78	10.208%	$51.5553	$51.56	$51.55	$51.60
Purchase #4	$56.95	5.190%	$59.9057	$59.91	$59.90	$59.90
Purchase #5	$130.70	8.720%	$142.097	$142.10	$142.10	$142.10
Purchase #6	$9.97	3.388%	$10.3078	$10.31	$10.30	$10.30
Purchase #7	$32.93	10.793%	$36.4841	$36.48	$36.50	$36.50
7 purchase totals =	$574.38		$625.6532	$625.67	$625.65	$625.70