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	$177.75	12.708%	$200.3385	$200.34	$200.35	$200.30
Purchase #2	$53.52	11.421%	$59.6325	$59.63	$59.65	$59.60
Purchase #3	$63.74	13.800%	$72.5361	$72.54	$72.55	$72.50
Purchase #4	$148.65	9.667%	$163.02	$163.02	$163.00	$163.00
Purchase #5	$40.76	9.329%	$44.5625	$44.56	$44.55	$44.60
Purchase #6	$172.84	9.275%	$188.8709	$188.87	$188.85	$188.90
Purchase #7	$119.63	10.602%	$132.3132	$132.31	$132.30	$132.30
7 purchase totals =	$776.89		$861.2737	$861.27	$861.25	$861.20