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	$54.73	8.704%	$59.4937	$59.49	$59.50	$59.50
Purchase #2	$6.40	6.311%	$6.8039	$6.80	$6.80	$6.80
Purchase #3	$50.98	7.320%	$54.7117	$54.71	$54.70	$54.70
Purchase #4	$188.91	4.217%	$196.8763	$196.88	$196.90	$196.90
Purchase #5	$136.70	7.389%	$146.8008	$146.80	$146.80	$146.80
Purchase #6	$195.77	8.519%	$212.4476	$212.45	$212.45	$212.40
Purchase #7	$117.38	12.700%	$132.2873	$132.29	$132.30	$132.30
7 purchase totals =	$750.87		$809.4213	$809.42	$809.45	$809.40