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	$74.83	13.257%	$84.7502	$84.75	$84.75	$84.80
Purchase #2	$78.39	5.538%	$82.7312	$82.73	$82.75	$82.70
Purchase #3	$232.25	10.424%	$256.4597	$256.46	$256.45	$256.50
Purchase #4	$105.33	7.747%	$113.4899	$113.49	$113.50	$113.50
Purchase #5	$64.70	10.248%	$71.3305	$71.33	$71.35	$71.30
Purchase #6	$41.73	6.725%	$44.5363	$44.54	$44.55	$44.50
Purchase #7	$204.43	12.260%	$229.4931	$229.49	$229.50	$229.50
7 purchase totals =	$801.66		$882.7909	$882.79	$882.85	$882.80