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	$185.93	10.578%	$205.5977	$205.60	$205.60	$205.60
Purchase #2	$183.74	9.139%	$200.532	$200.53	$200.55	$200.50
Purchase #3	$31.54	12.851%	$35.5932	$35.59	$35.60	$35.60
Purchase #4	$55.26	13.452%	$62.6936	$62.69	$62.70	$62.70
Purchase #5	$110.87	11.385%	$123.4925	$123.49	$123.50	$123.50
Purchase #6	$194.40	9.835%	$213.5192	$213.52	$213.50	$213.50
Purchase #7	$132.76	3.850%	$137.8713	$137.87	$137.85	$137.90
7 purchase totals =	$894.50		$979.2995	$979.29	$979.30	$979.30