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	$16.79	11.277%	$18.6834	$18.68	$18.70	$18.70
Purchase #2	$180.36	9.873%	$198.1669	$198.17	$198.15	$198.20
Purchase #3	$242.38	11.758%	$270.879	$270.88	$270.90	$270.90
Purchase #4	$73.59	11.869%	$82.3244	$82.32	$82.30	$82.30
Purchase #5	$163.33	5.315%	$172.011	$172.01	$172.00	$172.00
Purchase #6	$24.44	3.682%	$25.3399	$25.34	$25.35	$25.30
Purchase #7	$77.44	10.554%	$85.613	$85.61	$85.60	$85.60
7 purchase totals =	$778.33		$853.0176	$853.01	$853.00	$853.00