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	$66.96	8.403%	$72.5866	$72.59	$72.60	$72.60
Purchase #2	$57.50	7.842%	$62.0092	$62.01	$62.00	$62.00
Purchase #3	$145.87	7.122%	$156.2589	$156.26	$156.25	$156.30
Purchase #4	$169.33	12.700%	$190.8349	$190.83	$190.85	$190.80
Purchase #5	$20.92	11.687%	$23.3649	$23.36	$23.35	$23.40
Purchase #6	$202.60	7.776%	$218.3542	$218.35	$218.35	$218.40
Purchase #7	$99.71	13.321%	$112.9924	$112.99	$113.00	$113.00
7 purchase totals =	$762.89		$836.4011	$836.39	$836.40	$836.50