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	$179.61	7.184%	$192.5132	$192.51	$192.50	$192.50
Purchase #2	$202.47	9.554%	$221.814	$221.81	$221.80	$221.80
Purchase #3	$46.99	7.112%	$50.3319	$50.33	$50.35	$50.30
Purchase #4	$248.52	10.287%	$274.0853	$274.09	$274.10	$274.10
Purchase #5	$180.46	11.110%	$200.5091	$200.51	$200.50	$200.50
Purchase #6	$209.91	6.129%	$222.7754	$222.78	$222.80	$222.80
Purchase #7	$35.39	9.694%	$38.8207	$38.82	$38.80	$38.80
7 purchase totals =	$1,103.35		$1,200.8496	$1,200.85	$1,200.85	$1,200.80