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	$126.61	13.419%	$143.5998	$143.60	$143.60	$143.60
Purchase #2	$150.56	13.618%	$171.0633	$171.06	$171.05	$171.10
Purchase #3	$19.76	6.582%	$21.0606	$21.06	$21.05	$21.10
Purchase #4	$142.74	12.765%	$160.9608	$160.96	$160.95	$161.00
Purchase #5	$204.94	7.275%	$219.8494	$219.85	$219.85	$219.80
Purchase #6	$59.77	9.870%	$65.6693	$65.67	$65.65	$65.70
Purchase #7	$37.60	5.471%	$39.6571	$39.66	$39.65	$39.70
7 purchase totals =	$741.98		$821.8603	$821.86	$821.80	$822.00