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	$78.37	6.634%	$83.5691	$83.57	$83.55	$83.60
Purchase #2	$198.37	6.250%	$210.7681	$210.77	$210.75	$210.80
Purchase #3	$28.36	3.413%	$29.3279	$29.33	$29.35	$29.30
Purchase #4	$41.81	7.835%	$45.0858	$45.09	$45.10	$45.10
Purchase #5	$71.83	13.406%	$81.4595	$81.46	$81.45	$81.50
Purchase #6	$38.95	12.614%	$43.8632	$43.86	$43.85	$43.90
Purchase #7	$12.49	11.524%	$13.9293	$13.93	$13.95	$13.90
7 purchase totals =	$470.18		$508.0029	$508.01	$508.00	$508.10