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	$52.53	9.666%	$57.6075	$57.61	$57.60	$57.60
Purchase #2	$87.34	9.320%	$95.4801	$95.48	$95.50	$95.50
Purchase #3	$100.67	11.663%	$112.4111	$112.41	$112.40	$112.40
Purchase #4	$35.40	8.437%	$38.3867	$38.39	$38.40	$38.40
Purchase #5	$89.89	10.789%	$99.5882	$99.59	$99.60	$99.60
Purchase #6	$167.62	9.188%	$183.0209	$183.02	$183.00	$183.00
Purchase #7	$89.78	13.164%	$101.5986	$101.60	$101.60	$101.60
7 purchase totals =	$623.23		$688.0931	$688.10	$688.10	$688.10