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	$17.99	3.424%	$18.606	$18.61	$18.60	$18.60
Purchase #2	$174.36	3.202%	$179.943	$179.94	$179.95	$179.90
Purchase #3	$116.46	13.193%	$131.8246	$131.82	$131.80	$131.80
Purchase #4	$75.83	8.523%	$82.293	$82.29	$82.30	$82.30
Purchase #5	$229.40	10.516%	$253.5237	$253.52	$253.50	$253.50
Purchase #6	$116.55	3.572%	$120.7132	$120.71	$120.70	$120.70
Purchase #7	$240.97	13.855%	$274.3564	$274.36	$274.35	$274.40
7 purchase totals =	$971.56		$1,061.2599	$1,061.25	$1,061.20	$1,061.20