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	$81.29	10.224%	$89.6011	$89.60	$89.60	$89.60
Purchase #2	$210.49	5.447%	$221.9554	$221.96	$221.95	$222.00
Purchase #3	$122.35	12.380%	$137.4969	$137.50	$137.50	$137.50
Purchase #4	$84.88	5.752%	$89.7623	$89.76	$89.75	$89.80
Purchase #5	$204.36	8.457%	$221.6427	$221.64	$221.65	$221.60
Purchase #6	$47.85	7.521%	$51.4488	$51.45	$51.45	$51.40
Purchase #7	$152.38	12.235%	$171.0237	$171.02	$171.00	$171.00
7 purchase totals =	$903.60		$982.9309	$982.93	$982.90	$982.90