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	$166.30	13.334%	$188.4744	$188.47	$188.45	$188.50
Purchase #2	$83.93	9.390%	$91.811	$91.81	$91.80	$91.80
Purchase #3	$194.78	10.587%	$215.4014	$215.40	$215.40	$215.40
Purchase #4	$17.48	5.199%	$18.3888	$18.39	$18.40	$18.40
Purchase #5	$97.44	12.186%	$109.314	$109.31	$109.30	$109.30
Purchase #6	$147.67	5.301%	$155.498	$155.50	$155.50	$155.50
Purchase #7	$178.50	10.110%	$196.5464	$196.55	$196.55	$196.50
7 purchase totals =	$886.10		$975.4340	$975.43	$975.40	$975.40