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	$172.67	5.340%	$181.8906	$181.89	$181.90	$181.90
Purchase #2	$80.98	11.673%	$90.4328	$90.43	$90.45	$90.40
Purchase #3	$49.51	6.803%	$52.8782	$52.88	$52.90	$52.90
Purchase #4	$236.59	4.722%	$247.7618	$247.76	$247.75	$247.80
Purchase #5	$32.85	8.461%	$35.6294	$35.63	$35.65	$35.60
Purchase #6	$65.32	11.872%	$73.0748	$73.07	$73.05	$73.10
Purchase #7	$31.87	9.375%	$34.8578	$34.86	$34.85	$34.90
7 purchase totals =	$669.79		$716.5254	$716.52	$716.55	$716.60