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	$37.37	13.736%	$42.5031	$42.50	$42.50	$42.50
Purchase #2	$166.77	8.267%	$180.5569	$180.56	$180.55	$180.60
Purchase #3	$186.59	3.167%	$192.4993	$192.50	$192.50	$192.50
Purchase #4	$178.60	6.542%	$190.284	$190.28	$190.30	$190.30
Purchase #5	$117.63	11.529%	$131.1916	$131.19	$131.20	$131.20
Purchase #6	$35.91	4.853%	$37.6527	$37.65	$37.65	$37.70
Purchase #7	$242.28	8.460%	$262.7769	$262.78	$262.80	$262.80
7 purchase totals =	$965.15		$1,037.4645	$1,037.46	$1,037.50	$1,037.60