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	$126.55	11.340%	$140.9008	$140.90	$140.90	$140.90
Purchase #2	$18.59	11.789%	$20.7816	$20.78	$20.80	$20.80
Purchase #3	$37.30	4.393%	$38.9386	$38.94	$38.95	$38.90
Purchase #4	$82.54	11.302%	$91.8687	$91.87	$91.85	$91.90
Purchase #5	$240.81	11.819%	$269.2713	$269.27	$269.25	$269.30
Purchase #6	$213.87	5.755%	$226.1782	$226.18	$226.20	$226.20
Purchase #7	$176.38	13.696%	$200.537	$200.54	$200.55	$200.50
7 purchase totals =	$896.04		$988.4762	$988.48	$988.50	$988.50