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	$188.52	5.328%	$198.5643	$198.56	$198.55	$198.60
Purchase #2	$201.86	10.303%	$222.6576	$222.66	$222.65	$222.70
Purchase #3	$82.63	10.817%	$91.5681	$91.57	$91.55	$91.60
Purchase #4	$5.89	13.156%	$6.6649	$6.66	$6.65	$6.70
Purchase #5	$80.72	12.392%	$90.7228	$90.72	$90.70	$90.70
Purchase #6	$43.63	7.578%	$46.9363	$46.94	$46.95	$46.90
Purchase #7	$9.94	12.434%	$11.1759	$11.18	$11.20	$11.20
7 purchase totals =	$613.19		$668.2899	$668.29	$668.25	$668.40