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	$126.40	8.496%	$137.1389	$137.14	$137.15	$137.10
Purchase #2	$227.88	3.833%	$236.6146	$236.61	$236.60	$236.60
Purchase #3	$160.39	7.167%	$171.8852	$171.89	$171.90	$171.90
Purchase #4	$180.75	5.200%	$190.149	$190.15	$190.15	$190.10
Purchase #5	$38.66	5.495%	$40.7844	$40.78	$40.80	$40.80
Purchase #6	$76.28	8.587%	$82.8302	$82.83	$82.85	$82.80
Purchase #7	$90.81	12.586%	$102.2393	$102.24	$102.25	$102.20
7 purchase totals =	$901.17		$961.6416	$961.64	$961.70	$961.50