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	$90.67	10.183%	$99.9029	$99.90	$99.90	$99.90
Purchase #2	$163.29	10.745%	$180.8355	$180.84	$180.85	$180.80
Purchase #3	$86.29	3.702%	$89.4845	$89.48	$89.50	$89.50
Purchase #4	$58.90	7.449%	$63.2875	$63.29	$63.30	$63.30
Purchase #5	$196.69	7.535%	$211.5106	$211.51	$211.50	$211.50
Purchase #6	$108.63	11.193%	$120.789	$120.79	$120.80	$120.80
Purchase #7	$84.47	13.619%	$95.974	$95.97	$95.95	$96.00
7 purchase totals =	$788.94		$861.7840	$861.78	$861.80	$861.80