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	$69.84	12.739%	$78.7369	$78.74	$78.75	$78.70
Purchase #2	$245.93	10.593%	$271.9814	$271.98	$272.00	$272.00
Purchase #3	$65.55	10.654%	$72.5337	$72.53	$72.55	$72.50
Purchase #4	$72.42	5.756%	$76.5885	$76.59	$76.60	$76.60
Purchase #5	$221.49	7.584%	$238.2878	$238.29	$238.30	$238.30
Purchase #6	$162.89	9.140%	$177.7781	$177.78	$177.80	$177.80
Purchase #7	$164.70	7.635%	$177.2748	$177.27	$177.25	$177.30
7 purchase totals =	$1,002.82		$1,093.1812	$1,093.18	$1,093.25	$1,093.20