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	$8.37	6.186%	$8.8878	$8.89	$8.90	$8.90
Purchase #2	$123.97	5.614%	$130.9297	$130.93	$130.95	$130.90
Purchase #3	$172.63	4.725%	$180.7868	$180.79	$180.80	$180.80
Purchase #4	$93.70	4.777%	$98.176	$98.18	$98.20	$98.20
Purchase #5	$184.91	3.767%	$191.8756	$191.88	$191.90	$191.90
Purchase #6	$246.76	5.155%	$259.4805	$259.48	$259.50	$259.50
Purchase #7	$112.43	13.487%	$127.5934	$127.59	$127.60	$127.60
7 purchase totals =	$942.77		$997.7298	$997.74	$997.85	$997.80