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	$206.79	7.741%	$222.7976	$222.80	$222.80	$222.80
Purchase #2	$181.77	6.513%	$193.6087	$193.61	$193.60	$193.60
Purchase #3	$174.76	11.374%	$194.6372	$194.64	$194.65	$194.60
Purchase #4	$213.65	12.612%	$240.5955	$240.60	$240.60	$240.60
Purchase #5	$82.65	9.468%	$90.4753	$90.48	$90.50	$90.50
Purchase #6	$142.79	12.329%	$160.3946	$160.39	$160.40	$160.40
Purchase #7	$141.93	12.360%	$159.4725	$159.47	$159.45	$159.50
7 purchase totals =	$1,144.34		$1,261.9814	$1,261.99	$1,262.00	$1,262.00