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	$77.93	7.258%	$83.5862	$83.59	$83.60	$83.60
Purchase #2	$183.91	13.602%	$208.9254	$208.93	$208.95	$208.90
Purchase #3	$196.58	8.493%	$213.2755	$213.28	$213.30	$213.30
Purchase #4	$39.45	7.255%	$42.3121	$42.31	$42.30	$42.30
Purchase #5	$187.38	7.514%	$201.4597	$201.46	$201.45	$201.50
Purchase #6	$54.86	8.746%	$59.6581	$59.66	$59.65	$59.70
Purchase #7	$97.93	11.870%	$109.5543	$109.55	$109.55	$109.60
7 purchase totals =	$838.04		$918.7713	$918.78	$918.80	$918.90