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	$82.63	8.293%	$89.4825	$89.48	$89.50	$89.50
Purchase #2	$198.65	3.610%	$205.8213	$205.82	$205.80	$205.80
Purchase #3	$206.70	13.366%	$234.3275	$234.33	$234.35	$234.30
Purchase #4	$109.66	6.601%	$116.8987	$116.90	$116.90	$116.90
Purchase #5	$121.44	13.473%	$137.8016	$137.80	$137.80	$137.80
Purchase #6	$202.97	3.494%	$210.0618	$210.06	$210.05	$210.10
Purchase #7	$82.29	11.554%	$91.7978	$91.80	$91.80	$91.80
7 purchase totals =	$1,004.34		$1,086.1912	$1,086.19	$1,086.20	$1,086.20