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	$95.98	4.479%	$100.2789	$100.28	$100.30	$100.30
Purchase #2	$37.39	7.808%	$40.3094	$40.31	$40.30	$40.30
Purchase #3	$76.99	11.195%	$85.609	$85.61	$85.60	$85.60
Purchase #4	$52.32	5.354%	$55.1212	$55.12	$55.10	$55.10
Purchase #5	$185.27	11.148%	$205.9239	$205.92	$205.90	$205.90
Purchase #6	$83.76	7.484%	$90.0286	$90.03	$90.05	$90.00
Purchase #7	$47.31	8.562%	$51.3607	$51.36	$51.35	$51.40
7 purchase totals =	$579.02		$628.6317	$628.63	$628.60	$628.60