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	$182.39	4.768%	$191.0864	$191.09	$191.10	$191.10
Purchase #2	$40.36	13.422%	$45.7771	$45.78	$45.80	$45.80
Purchase #3	$220.84	4.821%	$231.4867	$231.49	$231.50	$231.50
Purchase #4	$78.41	6.314%	$83.3608	$83.36	$83.35	$83.40
Purchase #5	$92.57	11.786%	$103.4803	$103.48	$103.50	$103.50
Purchase #6	$219.94	10.406%	$242.827	$242.83	$242.85	$242.80
Purchase #7	$154.49	9.289%	$168.8406	$168.84	$168.85	$168.80
7 purchase totals =	$989.00		$1,066.8589	$1,066.87	$1,066.95	$1,066.90