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	$78.31	3.429%	$80.9952	$81.00	$81.00	$81.00
Purchase #2	$75.84	8.851%	$82.5526	$82.55	$82.55	$82.60
Purchase #3	$81.28	5.720%	$85.9292	$85.93	$85.95	$85.90
Purchase #4	$64.38	12.508%	$72.4327	$72.43	$72.45	$72.40
Purchase #5	$143.57	6.390%	$152.7441	$152.74	$152.75	$152.70
Purchase #6	$238.81	13.736%	$271.6129	$271.61	$271.60	$271.60
Purchase #7	$76.28	7.409%	$81.9316	$81.93	$81.95	$81.90
7 purchase totals =	$758.47		$828.1983	$828.19	$828.25	$828.10