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	$78.57	5.457%	$82.8576	$82.86	$82.85	$82.90
Purchase #2	$75.58	3.256%	$78.0409	$78.04	$78.05	$78.00
Purchase #3	$69.39	10.452%	$76.6426	$76.64	$76.65	$76.60
Purchase #4	$144.41	4.520%	$150.9373	$150.94	$150.95	$150.90
Purchase #5	$186.31	6.564%	$198.5394	$198.54	$198.55	$198.50
Purchase #6	$65.76	11.753%	$73.4888	$73.49	$73.50	$73.50
Purchase #7	$95.32	5.851%	$100.8972	$100.90	$100.90	$100.90
7 purchase totals =	$715.34		$761.4038	$761.41	$761.45	$761.30