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	$111.67	10.831%	$123.765	$123.77	$123.75	$123.80
Purchase #2	$197.47	10.779%	$218.7553	$218.76	$218.75	$218.80
Purchase #3	$202.98	10.739%	$224.778	$224.78	$224.80	$224.80
Purchase #4	$81.49	8.272%	$88.2309	$88.23	$88.25	$88.20
Purchase #5	$234.35	8.177%	$253.5128	$253.51	$253.50	$253.50
Purchase #6	$60.26	12.716%	$67.9227	$67.92	$67.90	$67.90
Purchase #7	$114.90	7.870%	$123.9426	$123.94	$123.95	$123.90
7 purchase totals =	$1,003.12		$1,100.9073	$1,100.91	$1,100.90	$1,100.90