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	$198.69	12.156%	$222.8428	$222.84	$222.85	$222.80
Purchase #2	$19.50	7.346%	$20.9325	$20.93	$20.95	$20.90
Purchase #3	$35.45	3.243%	$36.5996	$36.60	$36.60	$36.60
Purchase #4	$28.81	7.656%	$31.0157	$31.02	$31.00	$31.00
Purchase #5	$33.43	12.488%	$37.6047	$37.60	$37.60	$37.60
Purchase #6	$68.80	13.444%	$78.0495	$78.05	$78.05	$78.00
Purchase #7	$139.67	10.151%	$153.8479	$153.85	$153.85	$153.80
7 purchase totals =	$524.35		$580.8927	$580.89	$580.90	$580.70