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	$16.63	10.300%	$18.3429	$18.34	$18.35	$18.30
Purchase #2	$59.31	5.420%	$62.5246	$62.52	$62.50	$62.50
Purchase #3	$162.25	11.850%	$181.4766	$181.48	$181.50	$181.50
Purchase #4	$229.73	4.846%	$240.8627	$240.86	$240.85	$240.90
Purchase #5	$203.59	13.667%	$231.4146	$231.41	$231.40	$231.40
Purchase #6	$19.82	9.297%	$21.6627	$21.66	$21.65	$21.70
Purchase #7	$6.99	13.473%	$7.9318	$7.93	$7.95	$7.90
7 purchase totals =	$698.32		$764.2159	$764.20	$764.20	$764.20