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	$38.37	11.872%	$42.9253	$42.93	$42.95	$42.90
Purchase #2	$234.45	5.188%	$246.6133	$246.61	$246.60	$246.60
Purchase #3	$54.88	10.626%	$60.7115	$60.71	$60.70	$60.70
Purchase #4	$169.86	4.797%	$178.0082	$178.01	$178.00	$178.00
Purchase #5	$190.96	4.390%	$199.3431	$199.34	$199.35	$199.30
Purchase #6	$27.94	3.114%	$28.8101	$28.81	$28.80	$28.80
Purchase #7	$172.43	3.835%	$179.0427	$179.04	$179.05	$179.00
7 purchase totals =	$888.89		$935.4542	$935.45	$935.45	$935.30