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	$196.77	11.210%	$218.8279	$218.83	$218.85	$218.80
Purchase #2	$111.80	4.404%	$116.7237	$116.72	$116.70	$116.70
Purchase #3	$148.77	9.417%	$162.7797	$162.78	$162.80	$162.80
Purchase #4	$111.25	11.386%	$123.9169	$123.92	$123.90	$123.90
Purchase #5	$239.34	4.239%	$249.4856	$249.49	$249.50	$249.50
Purchase #6	$72.53	11.524%	$80.8884	$80.89	$80.90	$80.90
Purchase #7	$35.53	12.698%	$40.0416	$40.04	$40.05	$40.00
7 purchase totals =	$915.99		$992.6638	$992.67	$992.70	$992.60