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	$140.96	6.572%	$150.2239	$150.22	$150.20	$150.20
Purchase #2	$234.86	10.626%	$259.8162	$259.82	$259.80	$259.80
Purchase #3	$33.51	3.157%	$34.5679	$34.57	$34.55	$34.60
Purchase #4	$6.38	6.725%	$6.8091	$6.81	$6.80	$6.80
Purchase #5	$164.98	9.599%	$180.8164	$180.82	$180.80	$180.80
Purchase #6	$156.90	7.261%	$168.2925	$168.29	$168.30	$168.30
Purchase #7	$83.93	6.703%	$89.5558	$89.56	$89.55	$89.60
7 purchase totals =	$821.52		$890.0818	$890.09	$890.00	$890.10