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	$76.26	3.160%	$78.6698	$78.67	$78.65	$78.70
Purchase #2	$156.89	11.296%	$174.6123	$174.61	$174.60	$174.60
Purchase #3	$49.48	3.795%	$51.3578	$51.36	$51.35	$51.40
Purchase #4	$143.36	4.738%	$150.1524	$150.15	$150.15	$150.20
Purchase #5	$213.74	12.369%	$240.1775	$240.18	$240.20	$240.20
Purchase #6	$144.64	13.833%	$164.6481	$164.65	$164.65	$164.60
Purchase #7	$69.76	9.334%	$76.2714	$76.27	$76.25	$76.30
7 purchase totals =	$854.13		$935.8893	$935.89	$935.85	$936.00