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	$77.67	3.300%	$80.2331	$80.23	$80.25	$80.20
Purchase #2	$187.30	6.209%	$198.9295	$198.93	$198.95	$198.90
Purchase #3	$199.46	8.815%	$217.0424	$217.04	$217.05	$217.00
Purchase #4	$210.69	3.433%	$217.923	$217.92	$217.90	$217.90
Purchase #5	$94.55	10.850%	$104.8087	$104.81	$104.80	$104.80
Purchase #6	$122.46	5.826%	$129.5945	$129.59	$129.60	$129.60
Purchase #7	$74.56	10.671%	$82.5163	$82.52	$82.50	$82.50
7 purchase totals =	$966.69		$1,031.0475	$1,031.04	$1,031.05	$1,030.90