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	$185.43	13.186%	$209.8808	$209.88	$209.90	$209.90
Purchase #2	$169.40	11.825%	$189.4316	$189.43	$189.45	$189.40
Purchase #3	$35.32	10.254%	$38.9417	$38.94	$38.95	$38.90
Purchase #4	$187.47	6.732%	$200.0905	$200.09	$200.10	$200.10
Purchase #5	$30.32	5.267%	$31.917	$31.92	$31.90	$31.90
Purchase #6	$141.45	13.314%	$160.2827	$160.28	$160.30	$160.30
Purchase #7	$78.37	6.168%	$83.2039	$83.20	$83.20	$83.20
7 purchase totals =	$827.76		$913.7482	$913.74	$913.80	$913.70