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	$109.76	9.180%	$119.836	$119.84	$119.85	$119.80
Purchase #2	$196.94	6.248%	$209.2448	$209.24	$209.25	$209.20
Purchase #3	$84.63	9.103%	$92.3339	$92.33	$92.35	$92.30
Purchase #4	$47.96	12.288%	$53.8533	$53.85	$53.85	$53.90
Purchase #5	$51.52	5.732%	$54.4731	$54.47	$54.45	$54.50
Purchase #6	$242.40	11.575%	$270.4578	$270.46	$270.45	$270.50
Purchase #7	$18.75	5.178%	$19.7209	$19.72	$19.70	$19.70
7 purchase totals =	$751.96		$819.9198	$819.91	$819.90	$819.90