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	$107.25	10.865%	$118.9027	$118.90	$118.90	$118.90
Purchase #2	$228.97	9.505%	$250.7336	$250.73	$250.75	$250.70
Purchase #3	$18.87	8.822%	$20.5347	$20.53	$20.55	$20.50
Purchase #4	$38.45	10.638%	$42.5403	$42.54	$42.55	$42.50
Purchase #5	$159.95	8.206%	$173.0755	$173.08	$173.10	$173.10
Purchase #6	$39.38	7.350%	$42.2744	$42.27	$42.25	$42.30
Purchase #7	$47.79	8.539%	$51.8708	$51.87	$51.85	$51.90
7 purchase totals =	$640.66		$699.9320	$699.92	$699.95	$699.90