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	$135.96	5.558%	$143.5167	$143.52	$143.50	$143.50
Purchase #2	$152.86	4.423%	$159.621	$159.62	$159.60	$159.60
Purchase #3	$163.44	4.834%	$171.3407	$171.34	$171.35	$171.30
Purchase #4	$242.93	9.403%	$265.7727	$265.77	$265.75	$265.80
Purchase #5	$132.60	7.584%	$142.6564	$142.66	$142.65	$142.70
Purchase #6	$212.26	5.329%	$223.5713	$223.57	$223.55	$223.60
Purchase #7	$59.79	13.446%	$67.8294	$67.83	$67.85	$67.80
7 purchase totals =	$1,099.84		$1,174.3082	$1,174.31	$1,174.25	$1,174.30