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	$243.81	12.313%	$273.8303	$273.83	$273.85	$273.80
Purchase #2	$163.54	10.817%	$181.2301	$181.23	$181.25	$181.20
Purchase #3	$192.83	12.274%	$216.498	$216.50	$216.50	$216.50
Purchase #4	$146.90	5.580%	$155.097	$155.10	$155.10	$155.10
Purchase #5	$100.77	8.863%	$109.7012	$109.70	$109.70	$109.70
Purchase #6	$199.32	11.632%	$222.5049	$222.50	$222.50	$222.50
Purchase #7	$72.40	13.756%	$82.3593	$82.36	$82.35	$82.40
7 purchase totals =	$1,119.57		$1,241.2208	$1,241.22	$1,241.25	$1,241.20