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	$240.64	13.502%	$273.1312	$273.13	$273.15	$273.10
Purchase #2	$242.93	13.417%	$275.5239	$275.52	$275.50	$275.50
Purchase #3	$231.92	10.434%	$256.1185	$256.12	$256.10	$256.10
Purchase #4	$200.72	13.865%	$228.5498	$228.55	$228.55	$228.50
Purchase #5	$193.32	8.233%	$209.236	$209.24	$209.25	$209.20
Purchase #6	$212.48	12.215%	$238.4344	$238.43	$238.45	$238.40
Purchase #7	$198.89	12.246%	$223.2461	$223.25	$223.25	$223.20
7 purchase totals =	$1,520.90		$1,704.2399	$1,704.24	$1,704.25	$1,704.00