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	$10.31	9.522%	$11.2917	$11.29	$11.30	$11.30
Purchase #2	$87.89	10.299%	$96.9418	$96.94	$96.95	$96.90
Purchase #3	$220.32	11.616%	$245.9124	$245.91	$245.90	$245.90
Purchase #4	$241.30	9.731%	$264.7809	$264.78	$264.80	$264.80
Purchase #5	$60.33	8.636%	$65.5401	$65.54	$65.55	$65.50
Purchase #6	$42.56	5.175%	$44.7625	$44.76	$44.75	$44.80
Purchase #7	$181.94	9.567%	$199.3462	$199.35	$199.35	$199.30
7 purchase totals =	$844.65		$928.5756	$928.57	$928.60	$928.50