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	$116.28	13.223%	$131.6557	$131.66	$131.65	$131.70
Purchase #2	$51.78	9.659%	$56.7814	$56.78	$56.80	$56.80
Purchase #3	$169.34	8.511%	$183.7525	$183.75	$183.75	$183.80
Purchase #4	$93.96	11.205%	$104.4882	$104.49	$104.50	$104.50
Purchase #5	$221.31	4.584%	$231.4549	$231.45	$231.45	$231.50
Purchase #6	$230.95	4.323%	$240.934	$240.93	$240.95	$240.90
Purchase #7	$135.29	5.235%	$142.3724	$142.37	$142.35	$142.40
7 purchase totals =	$1,018.91		$1,091.4391	$1,091.43	$1,091.45	$1,091.60