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	$39.85	3.871%	$41.3926	$41.39	$41.40	$41.40
Purchase #2	$60.45	3.764%	$62.7253	$62.73	$62.75	$62.70
Purchase #3	$33.41	11.540%	$37.2655	$37.27	$37.25	$37.30
Purchase #4	$201.57	9.597%	$220.9147	$220.91	$220.90	$220.90
Purchase #5	$100.57	12.402%	$113.0427	$113.04	$113.05	$113.00
Purchase #6	$59.64	11.838%	$66.7002	$66.70	$66.70	$66.70
Purchase #7	$42.28	6.526%	$45.0392	$45.04	$45.05	$45.00
7 purchase totals =	$537.77		$587.0802	$587.08	$587.10	$587.00