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	$35.81	13.410%	$40.6121	$40.61	$40.60	$40.60
Purchase #2	$136.94	13.116%	$154.9011	$154.90	$154.90	$154.90
Purchase #3	$7.28	13.803%	$8.2849	$8.28	$8.30	$8.30
Purchase #4	$201.53	10.221%	$222.1284	$222.13	$222.15	$222.10
Purchase #5	$82.96	8.254%	$89.8075	$89.81	$89.80	$89.80
Purchase #6	$16.58	10.164%	$18.2652	$18.27	$18.25	$18.30
Purchase #7	$219.78	9.592%	$240.8613	$240.86	$240.85	$240.90
7 purchase totals =	$700.88		$774.8605	$774.86	$774.85	$774.90