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	$122.67	11.720%	$137.0469	$137.05	$137.05	$137.00
Purchase #2	$231.49	4.847%	$242.7103	$242.71	$242.70	$242.70
Purchase #3	$33.84	10.184%	$37.2863	$37.29	$37.30	$37.30
Purchase #4	$171.89	11.543%	$191.7313	$191.73	$191.75	$191.70
Purchase #5	$184.31	12.159%	$206.7203	$206.72	$206.70	$206.70
Purchase #6	$183.55	3.636%	$190.2239	$190.22	$190.20	$190.20
Purchase #7	$72.39	9.581%	$79.3257	$79.33	$79.35	$79.30
7 purchase totals =	$1,000.14		$1,085.0447	$1,085.05	$1,085.05	$1,084.90