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	$123.40	10.429%	$136.2694	$136.27	$136.25	$136.30
Purchase #2	$140.65	10.736%	$155.7502	$155.75	$155.75	$155.80
Purchase #3	$214.38	10.324%	$236.5126	$236.51	$236.50	$236.50
Purchase #4	$209.82	6.643%	$223.7583	$223.76	$223.75	$223.80
Purchase #5	$166.66	6.490%	$177.4762	$177.48	$177.50	$177.50
Purchase #6	$80.41	9.531%	$88.0739	$88.07	$88.05	$88.10
Purchase #7	$73.49	12.358%	$82.5719	$82.57	$82.55	$82.60
7 purchase totals =	$1,008.81		$1,100.4125	$1,100.41	$1,100.35	$1,100.60