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	$95.31	9.508%	$104.3721	$104.37	$104.35	$104.40
Purchase #2	$153.72	4.468%	$160.5882	$160.59	$160.60	$160.60
Purchase #3	$144.81	12.412%	$162.7838	$162.78	$162.80	$162.80
Purchase #4	$99.83	5.858%	$105.678	$105.68	$105.70	$105.70
Purchase #5	$129.87	3.264%	$134.109	$134.11	$134.10	$134.10
Purchase #6	$147.98	5.651%	$156.3423	$156.34	$156.35	$156.30
Purchase #7	$140.86	4.636%	$147.3903	$147.39	$147.40	$147.40
7 purchase totals =	$912.38		$971.2637	$971.26	$971.30	$971.30