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	$81.99	11.297%	$91.2524	$91.25	$91.25	$91.30
Purchase #2	$109.62	3.162%	$113.0862	$113.09	$113.10	$113.10
Purchase #3	$81.74	10.686%	$90.4747	$90.47	$90.45	$90.50
Purchase #4	$205.26	8.381%	$222.4628	$222.46	$222.45	$222.50
Purchase #5	$82.51	6.289%	$87.6991	$87.70	$87.70	$87.70
Purchase #6	$197.99	8.349%	$214.5202	$214.52	$214.50	$214.50
Purchase #7	$89.90	10.314%	$99.1723	$99.17	$99.15	$99.20
7 purchase totals =	$849.01		$918.6677	$918.66	$918.60	$918.80