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	$113.73	12.788%	$128.2738	$128.27	$128.25	$128.30
Purchase #2	$144.64	13.863%	$164.6914	$164.69	$164.70	$164.70
Purchase #3	$232.89	12.445%	$261.8732	$261.87	$261.85	$261.90
Purchase #4	$6.96	7.629%	$7.491	$7.49	$7.50	$7.50
Purchase #5	$183.99	13.601%	$209.0145	$209.01	$209.00	$209.00
Purchase #6	$104.92	10.714%	$116.1611	$116.16	$116.15	$116.20
Purchase #7	$210.77	6.270%	$223.9853	$223.99	$224.00	$224.00
7 purchase totals =	$997.90		$1,111.4903	$1,111.48	$1,111.45	$1,111.60